The baby boom cohort refers to Americans born between mid-1946 and mid-1964 — an 18-year period of sustained elevated fertility following World War II. Two features distinguish the baby boom from earlier post-war fertility spikes: the sheer number of births (peaking at 4.3 million per year in 1957, a level not exceeded again until 1989) and the duration of elevated fertility (18 years, vs. only 2 years after World War I (WWI)). The cohort has driven successive structural shifts in the U.S. age distribution as it has moved from youth dependency through peak labor force participation and is now entering mass retirement.
Birth rates rose sharply from under 24/1,000 population in 1945 to 26.5/1,000 in 1947, then remained elevated through 1964. This followed the return of servicemen, economic prosperity, and social norms favoring early family formation. Unlike subsequent fertility upticks (the echo boom was driven by population scale, not per-woman fertility), the baby boom reflected genuinely high completed fertility — families with 3–4 children rather than 1–2.
The baby boom cohort functions as a demographic bulge moving through the age pyramid:
Old-age dependency drives Social Security and Medicare fiscal pressure. Each additional older resident relative to working-age adults either requires higher payroll tax rates or lower benefit levels to maintain program balance. The boomer retirement wave is the dominant near-term driver of Old Age, Survivors, and Disability Insurance (OASDI) and Medicare trust fund depletion timelines — more so than medical cost growth (which affects the cost per beneficiary) or mortality trends (which affect duration of benefit collection).
Disability Insurance (DI) application rates peak among workers aged 50–64 — precisely the baby boomers' primary labor force years from the 1990s through the 2010s. The demographic bulge moving through high-application ages is the dominant structural driver of DI roll growth in the 1988–2010 period, per both the Pattison-Waldron (2013) incidence decomposition (90% demographic) and the Ruffing (2014) five-factor count accounting (78% demographic). As boomers age into Medicare/Old Age and Survivors Insurance (OASI) eligibility and exit the DI-eligible population, this mechanical demographic pressure recedes — consistent with the post-2010 DI enrollment decline documented by Deshpande et al. (2025). See DI Growth Decomposition.
The Long-Term Actuarial Balance (LTAB) shortfall is substantially a boomer-cohort artifact. The 1983 Greenspan Commission reforms were sized to pre-fund the boomer retirement wave; whether those pre-funded reserves prove sufficient depends on realized mortality (how long boomers collect) and on what birth cohorts replace them in the workforce (fertility and immigration assumptions). See Long-Term Actuarial Balance.
Boomers are disproportionately non-Hispanic White. As this cohort ages out, the overall U.S. population diversifies faster than immigration or minority birth rates alone would imply. This compositional shift has downstream implications for health disparities, disability program demographics, and political economy of social insurance.