The population growth in Pakistan started from its inception with a decline in the death rate for a longer period of time. After that expansion in population got accelerated with the declining mortality rate as a result of improvements in health and living standards of the people. Lower outbreaks of diseases and no famines were other factors in the declining mortality rate. The population by 1950 was calculated as 38 million in Pakistan. Today, the overall population has increased up to 200 million. 

The growth in population is expected to be continued for the forthcoming several decades. The projection in increasing population is expected to be observed in multiplier effect having tenfold up to 2100. This increased population will have clear implications for development in social and economic aspects. On the basis of projections made by Bongaarts, Sathar, and Mahmood (2013) in light of the projections of the United Nations, National Institute of Population Studies (NIPS)  and Population Council of Pakistan, the following sections of this piece of writing will discuss the future trends and dimensions of Population in Pakistan and its impacts on economic development.
From 1950 to 2010, the population increased five-fold reaching up to 174 million. By 2050, the analysis of the projections of population by UN, NIPS, and Population Council shows a projected population will be more than 300 million. The total fertility rate considered in the above projection was 2 births per woman in 2050. However, Pakistan Demographic and Health Survey in 2006-07 and NIPS in 2008 estimated a total birth rate of around 4 births per woman.

Bongaarts, Sathar, and Mahmood (2013) carried out their study and found that the population in 2050 will be reaching up to 395 million. Their analysis revealed that in the future a relatively small variation in fertility trends will have a large impact on population trends. The levels and trends in the age composition have significant effects on socio-economic development in the sectors of education, employment, poverty, and health. It is reported that from 1950 to 2000 the Pakistani population was very young were about 60 percent of the population was below 25 and during the century the age structure was slightly changed. However, huge changes in age structure are expected to be persisted in the forthcoming decades because of the decline in fertility and younger generations will be a smaller segment of the population than older generations.
The population below age 15 is small in population size due to a decline in fertility after the 1990s. The size of the population of age 65 and above is small but growing due to increased life expectancy. The population of age from 15 to 64 is large in number and growing at a fast pace. In the future, profound growth in the projected working-age population shows an opportunity as well as a challenge. If they are given opportunities to be employed then the economy of the country will be improved. Otherwise, if a large number of working people will be unemployed then severe negative social, economic, and political repercussions will likely be experienced. The anticipated population growth in the future depends upon four demographic trends namely high fertility, declining morality, population momentum from young age structure, and migration.

High Fertility
High fertility is said to be persisted when it goes beyond the replacement level of 2.1 births per woman. The replacement is a significant factor in the trends of population because it equalizes fertility level that if it maintained for a longer period of time then it produces zero population growth. Positive deviation from the replacement leads towards population growth and negative deviation leads towards decline. At present in Pakistan, replacement exceeds up to 2.3. Throughout history, the positive deviation has been observed to be persisted. It has been observed that fertility has been approached up to 7 births per woman in the 60s. Current and projected levels are going beyond replacement. Thus, high fertility will be a contributing force in population growth till 2050.
Declining mortality
In past, one of the factors in the increased population in Pakistan is a speedy decline in mortality rate. In Pakistan, life expectancy has improved at an encouraging level from 41 to 65 in the 50s. Advancement in medical and public health technology, improved standards of living, and nutrition contributed to enhancing life expectancy. In the forthcoming decade, life expectancy is expected to be increasing up to 72 by the year 2050 resulting decline in mortality.

Population momentum from a young age structure
For a certain period of time in the countries where the population is growing rapidly, the negative deviation from replacement level will not decline in population growth because of the young age structure due to high fertility and rapid population growth in the past years.  Thus, in Pakistan, this situation of the increasing population under 25 will persist. The large size of young aged people will result in a relatively increased birth rate that will be higher than the death rate even if fertility is at replacement. Such type of future growth is called population momentum which can be controlled if the young people marry later and take time to their first birth. The trend gets changed that young people in Pakistan will prefer smaller families than earlier generations, but that will not be uniform. Comparatively high educated youngsters particularly women are likely to have lower fertility than earlier generations. However, uneducated individuals will not deviate much as compared to their parents.

Migration
Some tangible effects can be seen in some countries due to international migration. In the case of Pakistan very slight out-migration is estimated as 1 per thousand people. 
The analysis of the four factors reveals that in Pakistan high fertility is dominating element in population growth. The standard projection goes up to 302 million in 2050 on the basis of 174 million in 2010. On the other hand, the replacement projection shows a population of just 264 million. This difference in projections is because of high fertility which was measured in absolute terms as 38 million. Even if the replacement fertility is taken from the existing situation, still the population is expected to grow at 53 percent in the forthcoming four decades. The young age structure will affect population growth by about more than half between now and 2050 where effects of mortality and migration will affect at a negligible percentage in comparison to young age structure. 
Afzal (2009) found that population growth severely affects economic development. For Pakistan, rapid population growth is a real and important problem because Pakistan has the highest total fertility in Asian countries. A highly increased population has become a key factor to reach the overall development goals. It is highly desirable this uncontrolled population growth is monitored to release the pressure on the existing infrastructure the returns of economic development are consumed by high population growth. The situation of Pakistan is different from other developed countries because the population growth and economic development are divergent. 

Human resources cannot be exported to other countries as already a huge number of Pakistanis are working abroad. Because of high population growth, national saving rates are affected where resources for reproductive purposes are diverted to meet the needs of the high population. Pakistan has the very lowest saving rates in Asia.

Foreign investment and export promotion policies of Pakistan have been fairly successful due to which Pakistan needs foreign aid on a concessional basis which is not available. That is why the government in the last decades offered varying incentives for foreign investment. Pakistan has the potential to cash human capital, advanced technology, technical skills, marketing expertise, employment generation, and linkages with other countries.

In Pakistan, the population under 15 has a large number that is dependent on hindering economic growth and they must be supported financially to be an active labor force. Saving rates are low which affects investment exercise. Living standards of the people fall due to severe effects on the productive efficiency of the working force. Pakistan encounters serious environmental problems. Highly increased population and impressive GDP puts pressure on natural resources while levels of pollution are increasing day by day. The fast pace of expanding industrial production and urbanization leads to industrial waste, water pollution, solid waste, and vehicle emissions that have resulted in serious health problems in many areas of the country. 
A close relationship between rapid population growth and poverty has been noted. With meager employment opportunities, relative and absolute poverty is persistent for a longer period of time. It is evident that poverty declined in the 1970s and 1980s but increased after the 1990s which badly affected poor families' demand for education, health, and housing needs. More recent evidence on the incidence of poverty indicates that poverty that declined in the 1970s and 1980s increased in the 1990s. 

That have adversely affected the poor families' demand for education and the health and housing conditions have also deteriorated. The issue of poverty in Pakistan has been always a challenge for sustainable development. Long-lasting economic development is not possible without protecting the rights of the vulnerable groups and the participation of the entire population in the development process.  Since speedy economic growth and population growth are incompatible and thus, population growth must be reduced on a war footing.
References
Bongaarts, J., Sathar, Z. A., & Royan, R. (2013). Capturing the demographic dividend in
Pakistan. Population Council, Inc. retrieved August 15, 2018, from https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2326-4624.2013.tb00005.

Afzal, M. (2009). Population Growth and Economic Development in Pakistan. The Open
Demography Journal. 2009, 2, 1-7. Retrieved August 16, 2018, from https://pdfs.semanticscholar.org/d054/5becd3d0ba01601f21103cdf8556513b2a29.pdf