Millennials have surpassed Baby Boomers as the nation’s largest living generation, according to population estimates released this month by the U.S. Census Bureau. Millennials, whom we define as those ages 18-34 in 2015, now number 75.4 million, surpassing the 74.9 million Baby Boomers (ages 51-69). And Generation X (ages 35-50 in 2015) is projected to pass the Boomers in population by 2028.

The Millennial generation continues to grow as young immigrants expand its ranks. Boomers – whose generation was defined by the boom in U.S. births following World War II – are older and their numbers shrinking as the number of deaths among them exceeds the number of older immigrants arriving in the country.

Generations are analytical constructs, and developing a popular and expert consensus on what marks the boundaries between one generation and the next takes time. Pew Research Center has established that the oldest “Millennial” was born in 1981. The Center continues to assess demographic, attitudinal and other evidence on habits and culture that will help to establish when the youngest Millennial was born or even when a new generation begins. To distill the implications of the census numbers for generational heft, this analysis assumes that the youngest Millennial was born in 1997.

Here’s a look at some generational projections:

Millennials

With immigration adding more numbers to its group than any other, the Millennial population is projected to peak in 2036 at 81.1 million. Thereafter the oldest Millennial will be at least 56 years of age and mortality is projected to outweigh net immigration. By 2050 there will be a projected 79.2 million Millennials.

Generation X

For a few more years, Gen Xers are projected to remain the “middle child” of generations – caught between two larger generations of the Millennials and the Boomers. They are smaller than Millennials because the generational span of Gen X (16 years) is shorter than the Millennials (17 years). Also, the Gen Xers were born during a period when Americans were having fewer children than later decades. When Gen Xers were born, births averaged around 3.4 million per year, compared with the 3.9 million annual rate during the 1980s and 1990s when Millennials were born.
Though the oldest Gen Xer is now 50, the Gen X population will still grow for a few more years. The Gen X population is projected to outnumber the Boomers in 2028 when there will be 64.6 million Gen Xers and 63.7 million Boomers. The Census Bureau projects that the Gen X population will peak at 65.8 million in 2018.

Baby Boomers

Baby Boomers have always had an outsized presence compared with other generations. They were the largest generation and peaked at 78.8 million in 1999.
There were an estimated 74.9 million Boomers in 2015. By midcentury, the Boomer population will dwindle to 16.6 million.

This post was originally published on Jan. 16, 2015, and updated on April 25, 2016, to indicate that Millennials have officially surpassed Baby Boomers in population.

Richard Fry is a senior researcher focusing on economics and education at Pew Research Center.