1 Introduction

Bangladesh has one of the greatest population densities of any country. It has additional residents there every day. More than two million individuals are added to the population of our nation every year. It has grown to be a serious problem for us. The greatest problem facing our country is this one. This problem has been being now gotten out of hand. In general, a country's population changes from having elevated rates of fertility and mortality to having low and steady levels of both factors [1]. This is referred to as a shift in demographics [2]. During the DT process, there are several changes in the population's size and age distribution, which lead to a variety of benefits in terms of demographics, society, and the economy, as social, and policy challenges [3,4,5]. Demographers have referred to these chances as a "window of opportunities." The opportunity window for demographics, however, is transitory and does not immediately result in a demographic dividend (DD). Countries will benefit from the demographic dividend DD if they use this window of opportunity by wisely allocating their funds to infrastructure and human resource development. Populations go through a phase of DT when there is an increase in the working-age population when children born during the preceding high fertility era reach that age. Declining fertility conduct to a corresponding decline in the child dependence ratio, which frees up money for family welfare and economic growth by lowering the demand for spending on children's health and education [6, 7]. Since old age is still some time off, the DT can be considered as a "window of opportunity" for the majority of countries. If families make more investments in their children's health, education, and human capital development, the productivity of the larger labor force will grow.

This will also increase the number of taxable adults per dependent, which will reduce the need for public schools and other services [8,9,10,11]. Building up human capital is crucial if you want to benefit from the demographic shift. If countries can manage the conditions brought on by the demographic shift, fast economic increase and human development happen [12, 13]. Anyway, it is not a given that the opening of the demographic window of opportunity would immediately result in economic growth. If the nation is unable to efficiently employ the increasing number of people in working age as human capital [11, 14, 15]. Commentators have emphasized the importance of demographic factors in both politics and development, citing the growing "youth bulges" in the Arab world as a major factor in the current "Arab Spring" [12]. Additionally, there is an inevitable "end-game" scenario associated with the demographic dividend, which occurs when the percentage of the population that is working age begins to decline and the percentage of the population that is elderly begins to increase. A recent study suggests that China may experience economic recession or stagnation very soon because of the aging working-age population throughout many industrialized countries, including Japan [5] and the closing demographic window of opportunity. Although Bangladesh is a traditional agrarian culture with limited resources and inadequate infrastructure, in just four decades, it has achieved remarkable progress in reducing both mortality and fertility. The nation is a good example of how demographic changes happened despite very slow economic growth and some unfavorable socio-economic, demographic, and political circumstances. These conditions include a low age at marriage for females (86% are married by age 20, with a median age at marriage of 16 years), a very low level of education, political unrest, corruption, a lack of law and order, natural disasters like floods, and a young age structure due to historically high fertility. It is also one of the countries with the densest populations and the seventh most populous nation in the world. The population of nearly 156 million people lives in a comparatively small area of 147,570 square kilometres [8]. With 1060 people per square kilometer, Bangladesh's population density is already five times higher than any other "mega" nation [16]. Its population density is about five times higher than Pakistan's and India's, respectively. Despite all of these negative socioeconomic, political, and environmental factors, the nation has managed to escape the "Malthusian trap" by raising food production, exporting human capital, putting women to work in labor-intensive industries, industrializing gradually but steadily—particularly in the apparel sector—lowering fertility rates, and improving child survival. With a per capita income of $1314 in 2015, the nation fell into the lower middle-income category and announced its intention to reach middle-income status by 2021. This essay's goal is to investigate the demographic change taking place in Bangladesh and its implications for the age distribution of the country's population. The study also explores the policy options that Bangladesh should utilize to best take advantage of the potential presented by the age structural change as well as the problems it poses.

2 Method and materials

Using time series data from national-level investigations and Bangladeshi population censuses, the study describes the DT in Bangladesh, which has been primarily driven by declining fertility and death rates. The next section looks at how the changing age shape of the population will affect Bangladesh's future developments between now and 2100.The many facets and effects of historical as well as future DT in Bangladesh have been described using country-specific population projection data from the World Population Prospects 2012 Revision released by the United Nations [8]. The Bureau of Statistics in Bangladesh has released its population forecasts. To the best of my knowledge, these projections are out of date because they were made using data from the 2001 population census and did not take into consideration the most recent demographic data on variables like mortality, fertility, and other factors. Moreover, the bulk of these projections have a constrained scope and time frame. In this context, the UN population forecasts are a better choice because they contain current data and cover a wide range of aspects related to Bangladesh's demographic shift, both past and future. There are two parts to the 2012 Revision of the United Nations population estimates and forecasts: historical estimates for the years 1950–2010 and future projections for the years 2010–2100. The present study, which corresponds to the median route for each component of a country's projected population, thus took into consideration projections for the preceding 70 years (1950–2020) and medium variant predictions for the next 80 years (2020–2100).

2.1 Theory of demographic transition

Some nations have already witnessed the DT, which is a normal process, while others are either going through it now or anticipate doing so shortly. This paper proposes an integrated framework approach that seeks to utilize the demographic dividend (DD) in development, using three theories: the DT theory, Ricardo's theory of comparative advantage, and Becker's human capital theory [13, 17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]. It also incorporates other crucial factors such as technological innovation and human capital to provide a comprehensive understanding of economic growth and development challenges, such as structural unemployment [33]. During the Second World War, demographics became an academic field, and since then, scholars have paid close attention to the demographic shift, especially in light of the decline in fertility and death rates [13]. The DT theory essentially offers a theoretical framework for deriving demographic predictions and interpreting historical population dynamics. A demographic uprising started in Europe in the late eighteenth century, extended to the rest of the globe in the nineteenth and twentieth centuries, and is still going on today. Illustrates the four basic phases of the DT, which is often a natural process that occurs from shifting population features. In preindustrial culture, the first phase is characterized by high rates of birth and mortality (especially among children). Improvements in diet, health, and medical knowledge caused death rates to begin to modestly drop during the pre-transition era, which is often referred to as the mortality or epidemiological transition. The second stage of the transition is characterized by a decreased mortality rate amid a high birth rate as a consequence of gradual improvements in food production, sanitation, and health. Moreover, a favorable correlation between affluence and reproductive success starts to appear, which encourages population growth. Lower fertility rates, which cause a decline in the pace of population expansion, signal the third phase, the late transition era. After a while, the mortality and birth rates eventually equalize at shortened stages, leading to little to no population increase.

2.2 Demographic dividend (DD) hypothesis

According to the DD theory [33, 34], the DD is a phenomenon that is mediated by a variety of factors, including labor supply, savings, and human capital. While a nation is reaching a low fertility and death rate and the number of the working masses is organically growing, the third phase of the demographic transition takes place. The percentage of people aged 0–14 years reduces definitively to 30% during this window of opportunity, while the number of those 60 and older declines to less than 15%. Since they make up a higher portion, people in the working age group may influence the economic progress of the country. For instance, East Asia was able to benefit from the "window of opportunity," and per capita income there climbed by more than 6% between 1960 and 1995. The baby boom generation is steadily and irreversibly aging, which lowers the dependence ratio of the non-dependent population. These are only a few of the methods that disperse the demographic benefit [23, 29, 35,36,37,38,39,40,41,42].

3 Results

3.1 The demographics of Bangladesh are evolving

At the beginning of the twentieth century, Bangladesh was home to less than 30 million people. The population grew at a rate of less than 1% per year until 1931 when it reached 35.3 million. After 1931, the population doubled every 40 years [10]. During the start of the current millennium, the country was home to about 130 million people. Bangladesh's entire population was estimated to be 150 million in 2011. That is precisely twice as many people as there were in 1971, the year the country gained independence from Pakistan after a nine-month liberation war. Thus, the population is increasing by nearly 2.0 million people a year at a growth rate of 1.37%. The speed of population expansion peaked in the 1950s and 1960s [10] (Fig. 1). The 1970s saw a brief decrease in the growth rate due to a hurricane in 1970, a famine in 1974, the three million-person, Liberation War in 1971, and other natural disasters [7, 16, 40]. The speed of population expansion was over 2% until the 1990s when it began to decline, and in the 2010s, it was just over 1%.

Fig. 1
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Total population (in millions) ad the speed of population expansion (%), 1950–2100 [8, 10]

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The sharp fall in fertility was the primary factor contributing to the population growth rates that began to decline in the 1990s and the steady but gradual decline in death rates. Bangladesh's rapid decline in fertility was attributed by most researchers to an efficient family planning program because the nation's socioeconomic conditions did not considerably improve during the study period [12, 39].The population will continue to rise in the next few years despite a persistent fall in the pace of growth because of the population's young age distribution. The country's total fertility rate (TFR) also plummeted, falling by three births per woman (or 48% of the TFR) in just two short decades, from 6.3 births per woman in the middle of the 1970s to 3.3 births per woman in the early 1990s [10, 18]. Even so, despite the continuous rise in the use of contraception, the TFR remained stable in the 1990s at about 3.3 births per woman. (Fig. 2). After a decade of stasis, the total fertility rate (TFR) began to decrease once more in the early 2000s, peaking at 2.7 births per woman in 2007 and 2.3 in 2011 [18, 28]. However, from 87 baby deaths per 1000 live births in 1993–1994 to 43 in 2011, the infant mortality rate has decreased [18, 20]. There was a downward trend in the rates of overall mortality, under-five mortality, infant mortality, and child mortality. Consequently, the life expectancy at birth has increased as well, rising from 55 years in 1981 to 68 years in 2011 [26]. Additionally, from 2.5% in 1974 to 1.4% in 2011, the population growth rates decreased. (Fig. 3) shows that a decline in fertility followed the drop in mortality, which is a typical pattern for demographic transition. The two factors that have changed the population of Bangladesh are, however, separated in time, which has sped up the population increase. The DT in Bangladesh appeared to be in its pre-transitional stage until the 1960s, according to data in [10]. Bangladesh entered the first stage of demographic change in the 1960s with a dramatic drop in mortality, but birth rates exhibited a moderate decline until the 1980s. Around 1980, as the fertility rate began to decline more quickly, Bangladesh entered its second demographic transition phase. Bangladesh is now at the beginning of the third phase of its population transition.

Fig. 2
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CPR and TFR in Bangladesh, 1975–2011 [10, 33]

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Fig. 3
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Trends in Bangladesh's (CBR) and (CDR) from 1950 to 2100 [33]

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Stage until the 1960s, according to data in [26]. Bangladesh entered the first stage of demographic change in the 1960s with a dramatic drop in mortality, but birth rates exhibited a moderate decline until the 1980s. Around 1980, as the fertility rate began to decline more quickly, Bangladesh entered its second demographic transition phase. Bangladesh's population transition is just now launching its third phase.

Make clear that Bangladesh's population growth rate was substantially lower before to the country's transition to democracy (up to the 1950s) than it is today. It is not implied by this that the fertility rate was lower than it is today [8] (Fig. 1). The high mortality and high fertility during that period caused the population growth rate to be substantially lower than 1% until 1931. The significant drop in death rates, which coincided with a slower-than-expected decline in fertility rates, led to a much greater pace of population expansion after 1950. When mortality increases and fertility declines until replacement level fertility is reached (i.e., the TFR reaches 2.1 births per woman), the age structure of the Bangladeshi population will continue to shift. If the death rate keeps going down, approaches the fertility rate, and both rates stay constant for an extended period, the population of Bangladesh will reach a stationary condition. Bangladesh's population will exceed 200 million in 2050, even if the country achieves replacement-level fertility in the first three years of the new millennium, as per the UN medium-variant population estimate (Table 1). 147,570 sq. km, or 1355 people per sq km, will contain a sizable population. Bangladesh is expected to exceed the limitations of its bio-capacity and ecological impact due to its enormous population. Due to the country's limited agricultural area, there won't be much room to increase food production because the country's population-to-land ratio would be almost saturated [7, 33] The population is expected to stabilize at 250 million by 2080, but the rate of population growth will continue to fall, possibly as low as 0.14 percent in 2050 [13]. The current analysis, which represents the median path for every segment of a nation's anticipated population, thus considered forecasts for the 70 years that preceded them (1950–2020) as well as medium variant estimates for the 80 years that followed (2020–2100).

Table 1 projections and estimates (medium variant) of the population's overall size (in millions), the number of women who are fertile (in millions), and the population's percentage by age group [8]
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3.2 Age-related structural change in Bangladesh

Age-structural transition (AST) is also known as age-structural alterations, is a crucial result of population change. A population pyramid is a useful and popular tool for graphically displaying a population's age-sex composition. The population pyramids for Bangladesh from 2000 to 2100 are shown in Fig. 4. The age pyramids in Fig. 4 show that the age structure has undergone a lot of changes and that these changes will continue as Bangladesh goes through its many demographic transitional stages. A pyramid that has a very broad base and rapidly tapers off towards the older age groups indicates that the population is young and in the early stages of demographic development. Such a typical age structure is indicated by Bangladesh's broad-based triangular population pyramids for the years 2000–2020. The age structure drastically changed between 2000 and 2020 due to the decline in mortality and gradually dropping fertility. The pyramids' shortened bases show that the number of children under the age of five decreased due to the steep decline in fertility that occurred during this time. From more than 13% in 2000 to roughly 9% in 2020, the percentage of kids under five years old dropped. Age groups 5–9 and 10–14 saw a similar decline in population throughout this time (Fig. 4). The projection results show that this process's intensity will continue to rise during the next forty years. The base of the population pyramid will shrink in both absolute and relative levels over this time. As a result, the age structure will no longer take the shape of a pyramid and will instead resemble a beehive or barrel. A population with low birth and death rates and a high percentage of people living in their later years will typically have a pyramidal structure. Due to the momentum of the previous high population growth, the working-age population (15–59 years) will rise in this scenario, and eventually, the elderly population (60 years and over) will also grow. Generally speaking, a population's age structure can be divided into four life-cycle stages, each with its unique economic ramifications. The four life cycle stages are infantile (age 0–14), young adult (15–24), mature (25–59), and old (60 +). The 0 to 14-year-old population is a financial burden to the family because children rely on adults in paid employment for their food, healthcare, education, and other social necessities. Although the demands of the young population between the ages of 15 and 24 differ from those of the younger population between 0 and 14, both groups experience expenses. The older working age group (25–59) is probably going to earn more money and save more of their income. However, the majority of the aged population relies on others for their food, healthcare, and other social necessities, which places a financial strain on the family. From 1950 to 2050, the age structural changes in Bangladesh for the four life cycle stages are shown in Table 1. The proportion of Bangladesh's population under 15 years old decreased from 44% in 1980 to 32% in 2010 as a result of a reduction in fertility that began in the early 1980s. According to UN projections, the proportion of children under 15 in the population will decrease even more and reach 17% in 2050. Such a drop in the dependent population will lessen the possible financial stress on families and create opportunities for Bangladesh to improve its human capital and provide high-quality childcare services. With a 20% proportion of the overall population, Bangladesh has seen a youth bulge (ages 15–24) since 1980. The youth share of the population is anticipated to decrease after 2020, after which it is anticipated to continue. However, until it stabilizes, the total number of young people will keep growing. Bangladesh is currently and will continue to encounter significant difficulties in providing for the requirements and needs of this enormous youth bulge. In 1980, Bangladesh's proportion of the population in the prime working age range of 25–59 years dropped to 31%. Since then, it has been rising, and it is predicted that this will continue until 2040 when approximately half of the population will be of legal working age. As has been the case since 1980, Bangladesh's population of people 60 years and older will continue to grow slowly but steadily. But as life expectancy rises beyond 2020, the increase will be quick and significant. The proportion of the elderly population will rise from 5.7% in 1980 to 8.1% in 2020 and 22.3% in 2050.

Fig. 4
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Population pyramids, Bangladesh, 2000–2100

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3.3 Bangladesh's opening up to new opportunities

Knowing a country's "window of opportunity" requires understanding AST in terms of the share of the four life cycle phases (ages < 15, 15–24, 25–59, and 60 +), as stated in the previous section, as well as the dependency ratio (DR) and the ageing index. A "demographic bonus or dividend" is produced by the decrease in the dependency ratio and rise in the population of prime working age during the AST. For the period 1950–2050, [8, 25] shows the total dependence ratio (TDR) and its components, including the child dependency ratio (CDR), elderly dependency ratio (EDR), relative contributions of CDR and EDR to TDR, prospective support ratio (PSR), and ageing index. The TDR and its elements illustrate how economically dependent and working-age people interact. The potential support ratio (PSR) measures "the extent to which individuals of working age (15–59) might be considered as supporting the elderly population (60 years of age or over) and is the ratio between the two" [25]. The PSR value shows how many people in working age are needed to assist each older person in the population. The population's rate of aging is shown by the ageing index.

The results in [8] demonstrate that Bangladesh's burden on the economically productive population remained high over the period 1950–1990 (more than 80%), primarily due to high fecundity. More than half of the population (those over 60 or under 15) at that time were children under the age of 15, accounting for over 90% of those who were dependent. Up until 2010, the EDR was only about 7%. But since 1990, TDR has been falling as a result of a decline in the number of children under the age of 15, and this trend is expected to last until 2030, when it will start to rise again, primarily as a result of an increase in the senior population [14]. The TDR has altered as a result of two conflicting trends: a decrease in the total population under 15 and an increase in the elderly population. Similar to the EDR, the PSR likewise stayed essentially unchanged in the neighbourhood of 9% until 2010, when it started to fall as a result of an increase in the aged population that outpaced the expansion of the economically active population. Since 2010, there has been a significant increase in the aging index, which is calculated as the proportion of dependent senior people (60 and older) to dependent children (ages 0–14). The aging index was 16.8 in 2000, and the projections indicate that it will rise to 129 in 2050, meaning that the number of elderly people will be nearly equal to the number of children under the age of 15 at that time [20, 32]. The supply of the labor force and human capital is the method through which the demographic dividend in a population happens. The development of human capital is immediately and directly impacted by decreased fertility and death. It gives families the chance to spend more money on their children's education, well-being, and nutrition, which will help to produce more highly skilled labor in the long run. By boosting the number of people who are working age and decreasing the dependence ratio, the demographic shift has an impact on the labor supply. As families get smaller, it also increases women's employment rates. An increase in the proportion of people in working age will have a significant demographic benefit for the economy. A larger percentage of workers, especially those in their prime working years, will lead to more capital accumulation because older employees prefer to save more, and younger people tend to spend more and take out loans[35]. Furthermore, workers who are in the prime of their careers are more likely to be paid more and, theoretically, more productive than those who are younger [13, 28].Here, Fig. 1 represents the total population (in millions) and the speed of population expansion (%), 1950–2100 and Fig. 2 represents CPR and TFR in Bangladesh, 1975–2011.

We know that,

$${\text{LFPR}}=\frac{\mathrm{Total Labour Force}}{\mathrm{Total Working Age Population}}\times 100$$

Bangladesh's labor force are participation rate (the percentage of people aged 15 or older who were currently employed) was estimated to be 58.2% in 2016–17, as Fig. 5 illustrates. The percentage of each sex in the labor force was 36.3% for women and 80.5% for men.

Fig. 5
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Total, child and elderly dependency ratios in Bangladesh, 1950–2050 [8, 25]

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The rate for rural areas was marginally higher than the rate for urban areas (55.7%), at 59.3%. Workers aged 30–64 had the highest labor force participation rates (68.4%), followed by those aged 15–29 (48.7%), and those aged 65 and beyond (31%) had the lowest rates.

3.4 Discussions and their relation to policy

Bangladesh has advanced to the third stage of the demographic transition (DT), according to the theoretical model. The demographic change in Bangladesh has roughly followed the same trends as those in Europe and many East Asian nations. This transformation has altered the population's age distribution significantly and given Bangladesh a window of opportunity. While many of the options are now obvious, in the future they will all become more so. If these opportunities are promptly and skilfully handled, the nation will reap enormous benefits. As previously mentioned, there is no guarantee of the bonus because of the short timeframe and the possibility of not all possibilities materializing. Bangladesh's window of opportunity started in the early 1980s and is expected to remain open until the late 2030s. Using the massive labor force, mobilizing savings and wealth, investing wisely in infrastructure, industry, and service development, and allocating the necessary funds for high-quality education, vocational training, and skill development training to produce high-quality human capital are all ways to capitalize on this window of opportunity. Based on the experience of many East Asian countries, recent studies have demonstrated that demographic transition may be used very effectively to achieve rapid economic development. East Asia's supposed "economic miracle" was made possible, in part, by demographic transition, according to Bloom and Williamson [30]. Across all life phases, the demographic shift creates new possibilities and problems. The number of children in Bangladesh under the age of 15 and their proportion in the population are both decreasing and will keep doing so in the future. On the other hand, the young population (aged 15–24) is growing in size and proportion. This presents a chance to enhance human capital via public policy initiatives targeted at enhancing healthcare, nutrition, and education. The AST offers a chance to enhance the scope and quality of education. Investments in children and young people's nutrition, education, and health will raise the standard of human capital since they will make up the majority of the future labor force. In this article Fig. 3 represents Trends in Bangladesh's (CBR) and (CDR) from 1950 to 2100 and Fig. 4 is expressed as population pyramids, Bangladesh, 2000-to 2100. For the next 15–20 years, Bangladesh will continue to experience a "youth bulge." This has pushed up the demand for higher education, healthcare, housing, and work possibilities and will continue to do so. By quickly developing job opportunities to keep pace with the rise in the labor supply, Bangladesh might take advantage of its rapidly growing workforce. If this isn't done, there will be a lot of bad things that happen, such as more unemployment and crime, as well as social and political turmoil. The amount and proportion of women working also rise throughout the window of opportunity. The demographic shift has an impact on family size as well as women's reproductive health and social standing. She will have more years without bearing children, have fewer children overall, and have the chance to raise her educational level. As a consequence, more women can and often are more eager to work to make a living, and they are more likely to put extra money into their children's education and health. By employing many female employees, most of whom are uneducated and untrained, in the expanding ready-made garment (RMG) sector, Bangladesh has already benefited economically. In terms of employment, profits from foreign currency, and contribution to GDP, the RMG industry has been essential to Bangladesh's economy since the 1990s (GDP). More than 4 million individuals, 90% of them are female laborers, are employed by it. It provides more than 10% of the GDP of the nation and 78% of export revenue. By giving women jobs and boosting their involvement in the labor force in the industrial and service sectors, Bangladesh would certainly have benefited from an increased demographic dividend.

Due to the demographic shift and rising life expectancy, Bangladesh's old population would grow both in number and proportion. Bangladesh will thus have to deal with issues with health care, retirement benefits, and social services for a large senior population. To overcome the obstacles, Bangladesh must create programs and policies that are acceptable. Because of this While the second DD is in effect, policies that it’s crucial to provide incentives to save money and build wealth at this stage components to make the most of this chance. Given Bangladesh's limited resources and job chances, skilled labor export might be a significant and feasible source of income, albeit this would result in a "brain drain" as the most talented individuals would leave the nation in pursuit of better economic prospects. "Brain drain" caused by the emigration of the skilled labor force is often mentioned as a significant human capital risk for most developing nations, although migrant labor is an essential aspect in the growth of many countries since it generates economic advantages via remittances. Bangladesh might take advantage of this opportunity by developing the skills of its working-age population by exporting them, given the enormous need for skilled labor in oil-rich and industrialized nations. As a result, there will be less strain on the domestic economy and unemployment rate, as well as an increase in remittances, socioeconomic growth at the national, community, and individual levels, and a decrease in population pressure. The growth of Bangladesh's economy and society has already benefited greatly from remittances. One of the top 10 nations that receive remittances is Bangladesh, according to the World Bank [30]. More than 7 million Bangladeshis are believed to be residing abroad as of the present, the majority of them are unskilled, according to World Bank estimates. When compared to the Bangladeshi population and labor market, the contribution of the Bangladeshi worker to the global economy is relatively modest. The export of skilled labor should be given higher priority by Bangladesh. To take advantage of the demands of the global labor market, the employability of its expanding workforce might be improved by offering training and via the educational curriculum. It is crucial to keep in mind that Bangladesh now has a window of opportunity, but it will close quickly and won't open again soon. The Bangladeshi government has to properly take advantage of the different possibilities brought about by demographic change. To expedite the demographic shift and take advantage of the window of opportunity presented by the age of structural change, policymakers must move swiftly to develop and put into place the necessary measures. The Bangladeshi government has to spend more money on training that will prepare people for jobs both domestically and internationally. The working population must be kept healthy and productive, which requires investment in health. For Bangladesh, it is crucial to have a relevant population strategy that promotes reduced fertility and creates the ideal demographics for long-term economic success. Bangladesh can develop into a successful nation by using the DD and enacting suitable policies. A nation might find itself in a "Malthusian trap" if adequate action is not taken, which would be detrimental to prospects.

If Bangladesh hopes to reap the benefits of the DD through efficient management of the demographic window of opportunity, it must give priority to improving health care, creating jobs and employment for the expanding working-age population, infrastructure development policies, and high-quality education. East Asian nations have previously shown how effectively managing the window of opportunity may turn a population boom into a population bonus and so support swift economic growth and development. The only method that is both affordable and successful for boosting human capital, eradicating poverty, and attaining long-term economic development is education. It increases people's potential for productivity and overall economic development International Institute of Applied Systems Analysis. For a nation to prosper socioeconomically, improvements in health and survival are crucial. Bangladesh has made significant progress in raising the net enrolment rate in primary schools, which is almost universal (94% in 2010), and has attained gender parity in school enrolment [26]. Nevertheless, the total enrolment rates at the secondary (less than 50% of the appropriate age group) and university levels (approximately 5% [7, 15, 43] continue to be low. A high dropout rate and a poor level of adult literacy are major problems for Bangladesh's education system. Around 30% of students in grades I through between 2008 and 2010 dropped out of school, according to data from the Bangladesh Bureau of Educational Information and Statistics [22]. According to [26], the adult population (15 + years) had a literacy rate of 59.8% in 2010, which means that a significant portion of the population—approximately 45 million people—is illiterate. High school dropout rates owing to poverty, managerial issues, and insufficient funding for the education sector are concerns facing the industry. To create human capital via high-quality education, Bangladesh now spends roughly 2% of its GDP on education, which is egregiously insufficient and has to be updated. In Bangladesh, the demand for higher education is rising due to sustained economic expansion, and during the last forty years, both the number of public and private institutions has multiplied. Bangladesh presently has 37 public universities and more than 70 private institutions, compared to only six public universities and no private universities in the early 1970s. Despite increased university enrolment and strong job development, there is a paradoxical high graduate unemployment rate that is often much higher than the overall unemployment rate.

In Bangladesh, 47% of graduates remain jobless, despite the country's general unemployment rate being approximately 5%, according to recent research on graduate unemployment in South Asia written by the Economist Intelligence Unit (2013). The research partially blames the nation's fast-growing but subpar private education industry and the usage of out-of-date curricula at public institutions for the graduate unemployment crisis. There is a lack of trained labor with particular specialties despite the vast number of graduates in a variety of topics from both public and private colleges. Despite the labor market's dire need for trained employees, graduate unemployment remains high. The country's secondary and higher education institutions are not churning out graduates with the skills demanded by the labor market, which helps to explain in part this seeming contradiction.

Bangladesh faces a difficult problem in creating employment due to its expanding population and modest economy. Since the nation's independence, the economy has undergone structural development. The economy steadily shifted from being agrarian to being more centered on industries and services. However, the economy's expansion has not been sufficiently followed by the creation of new jobs, and the number of unemployed individuals has risen over time. Building the infrastructure required for the health and survival of adults and children alike must be Bangladesh's top priority because it is essential to the country's economic growth, human capital development, and capital preservation. According to a recent study by [40] a higher child survival rate results in lower rates of reproduction and altruistic intergenerational transfers as well as higher rates of savings and productivity growth. Conversely, higher adult survival rates can also act as a substitute for experience and provide incentives for capital savings, which boosts labour productivity and spurs economic growth [39, 44,45,46,47,48,49], Finally, Fig. 5 represents the total, child and elderly dependency ratios in Bangladesh, 1950–2050, and also Fig. 6 expands the percentage of each age and gender in the labor force. The best asset Bangladesh has is its enormous human capital. Development programs should focus on a population that is already prepared to participate in the labor market and other economic activities, considering the nation's potential for human growth. The population's current demands must also be met by creating and sustaining an appropriate institutional framework, a favorable socio-political environment, and the implementation of pertinent and timely policies. The interaction between the population's makeup and prospects for economic growth and development is something that population planners must take into account.

Fig. 6
figure 6

percentage of each age and gender in the labor force [34]

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4 Conclusion

In conclusion, this study offers a methodology for examining the population projection's behavior. In particular, we develop predictions of population growth and DT in Bangladesh. Available actual and adjusted census data (1901–2022) of the Bangladesh population were Population size, CBR, CDR, natural growth rate, and annual growth rate in Bangladesh and projections and estimates (medium variant) of the population's overall size (in millions), the number of fertile women (in millions), and the population's percentage by age group. Therefore, policies should be developed to attain demographic advantage, taking into account the demographic problem as the primary concern of the Bangladeshi government. The proposed method is direct, concise, and effective for investigating more DT in Bangladesh. In the future, this method's solution could be beneficial for the Government of Bangladesh must take preventive measures and plan to avoid such essential outcomes, which is only possible if the Government of Bangladesh can control this.