The United States Census Bureau defines “baby boomers” as those people born between 1946 and 1964. The return of U.S. servicemen from World War II sparked a sudden rise in the national birth rate; 3.4 million babies were born in 1946, a 20-percent rise over the previous year. By the end of the baby boom era in 1964, the babies born in the period made up almost 40 percent of the population.

Population Pyramids

Population pyramids show the population of a country in graphic form. One aspect of the pyramid divides the population by sex; one side, typically the left, shows the male population and the other shows the female population. The vertical axis, meanwhile, sub-divides the population into a series of age “groups,” usually made up of five- or 10-year blocks. The pyramid narrows towards the top, as only a small proportion of people survive into very old age in comparison with the much larger number of babies born.

Changing Pyramids Over Time

Successive population pyramids show the progression of the baby boomer generation through time. Pyramids for 1960 show a pronounced “bulge” in the 0-14 age groups, in marked contrast to the “pinch” shown in the previous generation, when birth rates fell due to the Depression and World War II. By 1990, the baby boomers fell into the 25-44 age group but still produced a “bulge” in the pyramid’s shape.

Today

Today, the baby boomers have helped to alter the shape of the population pyramid into something resembling a rectangle, but the "bulge" they cause is not the only factor at work. Death rates have dropped significantly for all age groups during the baby boomers’ lifetimes; research carried out by the Centers for Disease Control and Prevention revealed that mortality risk fell by at least 50 percent for all age groups except the over-85s between 1935 and 2010. This limits the narrowing of the top of the pyramid. Meanwhile, birth rates have also fallen and, as of 2010, stand at 1.9 children per woman, narrowing the pyramid’s base.

Predictions

As the baby boomers move into old age, they will continue to influence the shape of the country’s population pyramid. A 2003 Library of Congress report suggested that U.S. life expectancy will continue to rise to 2050 and beyond; women aged 65 in 2025 can expect to live another 20 years, while men can expect an additional 17.5 years. As a result, the U.S. Census Bureau expects the baby boomer’s “bulge” to remain observable in the population pyramids for 2035, when the boomers will be aged between 70 and 90, and even as late as 2060, when the remaining boomers will be well into their nineties or even older.