NYC Population
Complete Analysis of U.S. Census Bureau Estimates for July 1, 2015
Introduction
The  U.S. Census Bureau prepares estimates of total population for all counties in  the United States on an annual basis, using a demographic procedure known as  the “administrative records method” (described below). This method assumes that  post-census population change can be closely approximated with vital statistics  data on births and deaths, along with other administrative and survey data that  provide a picture of migration patterns.
Total Population
According  to U.S. Census Bureau population estimates, New York City’s population  increased from 8,175,1331 in  April of 2010 to 8,550,405 in July of 2015. This is an increase of 375,300 residents  or about 4.6 percent over the 2010 mark. Among the boroughs, Brooklyn saw the largest  change in population in this 63-month period, growing by 5.3 percent or 132,000  persons, followed by the Bronx (5.1 percent or 70,300 persons), Queens (4.9  percent or 108,400 persons), and Manhattan (3.7 percent or 58,600 persons). The  lowest growth occurred in Staten Island (1.2 percent or 5,800 persons).
New  York City’s population increase since April of 2010 represented 89.8 percent of  the total increase in New York State, which raised the city’s share of the  State’s population, from 42.2 percent to 43.2 percent.
Components of Population Change
Demographers  divide population change into components.  Natural increase represents  the difference between births and deaths. Net migration represents the  balance between persons entering and leaving an area. Together, these  components describe how populations change over time. The U.S. Census Bureau  constructs population estimates for all counties in the United States by  separately estimating the components of change. Births and deaths are compiled  using data from the national vital statistics system. Net migration is  calculated by estimating the rate of net migration for persons coming in from  and leaving for other counties in the 50 states (net domestic migration)  and the balance of people who immigrate from and emigrate to other nations and  Puerto Rico (net international migration). The net domestic migration  rate is derived using income tax returns from the Internal Revenue Service and  Medicare enrollment data from the Social Security Administration (see methods  discussion below).
It is important to keep in mind that  New York City has a very dynamic population, with several hundred thousand  people coming and going each year. This “churn” has long characterized the City,  and represents a fluidity that is difficult to characterize using the net migration  measures presented herein. This dynamism is a testament to the City being a  magnet for those seeking opportunities, then moving on, only to be replaced by  the next set of individuals aspiring for a better life.  This very vibrant  picture is what makes New York City’s population extraordinary and different  from most other places in the nation and, perhaps, the world.
The most recent estimates from the U.S.  Census Bureau indicate the following for the 2010-2015 period:
a) Positive natural increase – the  surplus of births over deaths added 341,300 persons to New York City’s  population between April of 2010 and July of 2015.
b) Net migration was positive for  the city overall, with a net migration gain of 49,600 persons for the  period.  While small by the standards of the City’s overall population, the  picture of positive net migration represents a reversal of longstanding pattern  of population losses through migration. The recent gain through migration  was the result of a net inflow of 452,500 persons through international  migration, which offset a net domestic migration loss of 402,900 persons. For  the first time in over a half-century, migration fueled population growth.
c)   Every borough, except  Staten Island, displayed positive net migration between April 2010 and July of 2015. 
New Patterns of Recent Growth:  2014-2015 vs. 2010-2014
The  robust pace of growth in the post-2010 period has not been seen since the  1920s. However, the most recent 2014-2015 estimates point to a relatively lower  growth rate as compared to 2010-2014. The increase over the past year,  2014-2015 was 55,200 or 0.6 percent, compared to 75,300 or about 0.9 percent  annual average growth for the 2010-2014 period. 
In  the 2014-2015 period, Brooklyn experienced net outflows, a reversal of the  pattern in prior years. Growth in Brooklyn was at the City average (0.6 percent)  in the past year, while the Bronx (0.9 percent) and Queens (0.7 percent) had higher  than average growth. Indeed,  the Bronx had the highest growth of any county in New York State, while Queens  added the most people in numerical terms.
U.S. Census Bureau Population Estimates Methodology
Each  year, the U.S. Census Bureau produces estimates of the population for states,  counties, cities and other places, as well as for the nation as a whole. They  utilize data from a number of sources to estimate the change in the population  for each year since the most recent decennial census. These population  estimates use the 2010 Census counts as a base.
The U.S. Census Bureau subtracts the  number of resident deaths from the number of resident births annually for each  county in the U.S., to derive growth due to natural increase.  Births are tabulated by residence of the mother, regardless of where the birth  occurred. Similarly, deaths are tabulated by the most recent residence of the  decedent, not where the death occurred. Birth and death certificates from the  National Center for Health Statistics are used as the data source. The data on  births and deaths are generally considered to be the most reliable part of the  components of change analysis.
Net domestic migration represents the net exchange between  a county and other counties in the 50 states. This component is estimated for three  age groups (0-17, 18-64 and 65 years and older). For ages 0 to 64, the U.S. Census  Bureau uses data on filers and dependents from federal income tax returns  supplied by the Internal Revenue Service (IRS). In-migrants and out-migrants  between counties as well as non-movers are identified by comparing the  addresses of income tax filers from year-to-year to determine residence at two  points in time. For example, to produce the July 1, 2015 estimates, the  addresses of tax filers in 2013 and 2014 are compared. In-migrants to a county  were defined as those with an address in the county in 2014, but outside the  county in 2013; out-migrants are those with an address in the county in 2013,  but outside the county in 2014; and individuals who filed tax returns at the  same address at both points in time are non-migrants. Since every U.S. resident  may not file or be claimed as an exemption on a tax return, these data cannot  be used to directly estimate the number of county-to- county migrants.  Instead a net domestic migration rate needs to be calculated by taking  the difference between the numbers of in- and out-migrants (net-migrants) and  dividing it by the sum of the non-movers and out-migrants.2 Because many retired persons do not file tax returns, the U.S. Census Bureau uses  addresses from Medicare enrollment data in much the same way as they use IRS  data to determine domestic migration for the population 65 years and over.
Net International Migration is the result of net flows to and  from foreign countries and Puerto Rico and is estimated in the following parts:  immigration of the foreign-born, emigration of the foreign- as well as  native-born, and net migration between the U.S. and Puerto Rico.  Immigration of the foreign-born is estimated using the ACS question on  residence in the prior year. Foreign-born persons who indicated that they lived  abroad in the prior year are considered immigrants.
Emigration of the foreign-born is estimated  using the residual method. For example, the foreign-born population is aged  forward to obtain the expected population in the year 2015. The expected  population is then compared to the population estimated in the 2015 ACS.  Subtracting the estimated from the expected populations provides the  residual, which then serves as the basis of emigration rates for the foreign-born.  Emigration rates of the native-born are based on research by Schachter (2008)  using data from over 80 countries.3This work compares estimates of U.S. citizens living overseas measured for two  consecutive time periods and uses the difference to develop estimates of net  native migration.
1While there is little doubt that New York City has  experienced a substantial population increase post-2010, it is probably  overstated. Brooklyn and Queens likely experienced an undercount in the 2010  Census, the result of misclassifying housing units as vacant. A conservative  estimate is that this problem understated the population of the two boroughs by  65,000 persons. This means that the population of the city in 2010 was easily  in excess of 8,240,000 – and not the 8,175,100 base from the 2010 enumeration  that is used in the calculations of change.
See Salvo, J.J. and A.P. Lobo (2013). “Misclassifying New York’s Hidden Units as Vacant in 2010: Lessons Gleaned for  the 2020 Census.” Population Research and Policy Review, 32(5), 729-751.  http://link.springer.com/article/10.1007/s11113-013-9298-1
2 One reason  why small changes in estimates need to be interpreted with caution relates to  the effects that tumultuous events can have on the administrative data used to  create population estimates.  Such is the  case with super storm Sandy and its impact on the utility of tax return data to  estimate migration levels for the boroughs.
3 Schachter, Jason. 2008. “Estimating Native emigration from  the United States,” Memorandum dated December 24, delivered to the US. Census  Bureau.
This work compares estimates of U.S. citizens living overseas measured for two consecutive time periods and uses the difference to develop estimates of net native migration.
View Original PlaNYC Projections, 2000-2030
New York City Population Projections by Age/Sex and Borough, 2000-2030
Full Report (680 k) – A detailed analysis of the total population projected to 2030, as well as the projected school-age and elderly populations. Includes an in-depth description of the projection methodology.
Briefing Booklet (720 k) – an illustrated guide to the projection methodology and to the major findings.
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Visit PLANYC 2030 - Learn about the challenges New York City will face over the next 25 years -- and how you can help solve them.
Mayor Bloomberg's Sustainability Address - Mayor Michael R. Bloomberg cited DCP's population projections in his December 12, 2006 address regarding planning for a sustainable future.
City Planning Press Release: City Planning Demographers Paint Picture of City's Future Population At 9.1 Million, Detailing How City Will Grow By 2030.