American population

 Congressional Budget Office - The size of the U.S. population and its composition by age and sex have significant implications for the economy and the federal budget. For example, the number of people ages 25 to 54 affects the number of people who are employed, and the number of people age 65 or older affects the number of Social Security and Medicare beneficiaries...

• Population. The measure of population used in this report is the Social Security area population, which is relevant for estimating payroll taxes and benefits for Social Security. That population (which includes residents of U.S. states and territories, as well as U.S. citizens, federal employees, and service members living abroad) is projected to increase from 350 million people in 2025 to 372 million in 2055. The part of the population age 65 or older is projected to grow more quickly than younger groups, causing the average age of the population to rise.
• Population Growth. In CBO’s projections, the rate of population growth generally slows over the next 30 years, from an average of 0.4 percent a year between 2025 and 2035 to an average of 0.1 percent a year between 2036 and 2055. Net immigration becomes an increasingly important source of population growth. Without immigration, the population would shrink beginning in 2033, in part because fertility rates are projected to remain too low for a generation to replace itself.
• Civilian Noninstitutionalized Population. The number of people age 16 or older who are not on active duty with the armed forces or in institutions is used to project the size of the labor force. CBO produced two projections of that population using differing data from federal agencies. Both projections are consistent with CBO’s projections of overall population growth.
• Changes Since Last Year. ...Since last year, CBO has lowered its projection of the total fertility rate over the long run from 1.70 births per woman to 1.60 and incorporated differences in the fertility rates of women born in the United States and women born elsewhere. CBO also projects less net immigration in 2024 and most years thereafter than it projected last year. The change for 2024 largely reflects the consequences of a June 2024 executive order that temporarily suspended the entry of most noncitizens at the southern border.

CBO’s projections of fertility, mortality, and net immigration rates are highly uncertain. Small differences between those projections and actual outcomes could compound over time and significantly alter the demographic picture by the end of the 30-year projection period.