Boomer, Gen X, Millennial, Gen Z: the labels are everywhere, but the years behind them depend on who is counting. Here are the main definitions side by side, how big each group is today, and why the lines are less solid than they look.
Pew Research Center’s definitions are widely cited. Its January 2019 short read set the Millennial range at 1981–1996 and said anyone born from 1997 onward belongs to a new generation; its generations chart (May 2019) adds the Silent Generation, 1928–1945. Pew’s 2020 report on Gen Z defines it only as born after 1996, with no end year. The Census Bureau has used generation labels in some releases: when it announced in June 2015 that millennials outnumbered baby boomers, it defined millennials as born 1982–2000 and boomers as 1946–1964.
| Generation | Pew birth years | Census Bureau usage | U.S. residents, July 1, 2025 |
|---|---|---|---|
| Silent Generation | 1928–1945 | – | 14.7 million |
| Baby Boomers | 1946–1964 | 1946–1964 (used in 2015) | 66.6 million |
| Generation X | 1965–1980 | – | 64.4 million |
| Millennials | 1981–1996 | 1982–2000 (2015 release) | 73.1 million by Pew’s range; 87.5 million by Census’s |
| Generation Z | 1997 onward, no end year | – | 72.2 million for 1997–2012 |
| No official name | – | – | 50.6 million born 2013–2025 |
The two millennial definitions differ by a year at the start and four at the end, which is enough to change the count by 14.5 million. A 1999 birth is Gen Z to Pew and a millennial in the Census release. To check a single birth year against both, use the generation calculator.
The sizes in the table come from the Census Bureau’s Vintage 2025 estimates of the U.S. resident population by single year of age on July 1, 2025. The estimates are by age, not birth year, so this article takes birth year as 2025 minus age. That is an approximation: someone aged 30 on July 1, 2025 could have been born in the second half of 1994 or the first half of 1995, so each generation’s count can be off by part of a year at each end. People aged 100 and over are grouped together in the file and are left out. The total U.S. population in the file is 341.8 million.
By Pew’s ranges, Millennials are the largest living generation (21.4% of residents), ahead of Boomers (19.5%) and Gen X (18.8%). The largest single birth year among U.S. residents is about 2000, with 4.9 million people aged 25.
These are counts of people living in the U.S. now, not of births. They shrink as people die and grow with immigration. The Census Bureau’s 2015 release counted 75.4 million boomers; by the same 1946–1964 range the 2025 estimate is 66.6 million, about 8.8 million fewer. Its 1982–2000 millennials numbered 83.1 million in 2015 and about 87.5 million in 2025, 4.4 million more, even though nobody new was born into that range.
Only the baby boom has a demographic edge: Pew’s 2019 short read ties it to the surge in U.S. births after World War II in 1946 and the decline after 1964. The other lines are judgment calls. Pew said it ended Millennials at 1996 to keep the generation analytically meaningful, and because people born after that experienced the formative events of Millennials (the 9/11 attacks, the wars in Iraq and Afghanistan, the 2008 election and the Great Recession) at a different age or not at all.
In May 2023 Pew went further, saying a typical generation spans 15 to 18 years and that existing definitions may be too broad and arbitrary to capture differences within them, and set out how it would report on generations from then on. Applied to Gen Z, a 15- to 18-year span would end it with births somewhere between 2011 and 2014, but Pew has not set that year.
The cutoffs are not visible in the data. There were about 4.51 million U.S. residents aged 29 (born about 1996, Millennials) and 4.53 million aged 28 (about 1997, Gen Z) in 2025, a difference of 0.4%. Nothing about the people changes at the line.
Each generation spans a lot of life stages. Pew’s Boomer range covers 19 birth years: the oldest were 18 when the youngest were born. Averages for a whole generation can hide bigger differences inside it.
Age and generation get confused. A survey finding about “Gen Z” in 2025 describes people aged 13 to 28, so a difference from older groups may reflect age as much as generation.
Different reports use different years. A headline about millennials may use Pew’s 1981–1996, the Census Bureau’s 1982–2000 or a marketer’s own range. Compare like with like, and check whether the count is of births or of people living in the U.S. today.
Cusp years are not a separate generation. Some writers call people born around 1977–1983 “Xennials”; Pew does not. About 29.7 million U.S. residents fall in those seven birth years.
“Gen Alpha” is widely used for today’s children, but it is not officially defined by Pew or the Census Bureau, and Pew has not said where Gen Z ends. Until it does, a child born in 2015 is Gen Z by Pew’s published definition. About 50.6 million U.S. residents were born from 2013 through mid-2025. If you need someone’s exact age rather than a label, the age calculator counts it to the day. Schools draw their own birth-date lines: most states admit a child to kindergarten if they turn 5 by a cutoff such as September 1, and the kindergarten age calculator applies each state’s date.
Pew Research Center: Defining generations (January 17, 2019); The generations defined (May 14, 2019); What we know about Gen Z so far (May 14, 2020); How Pew Research Center will report on generations moving forward (May 22, 2023). U.S. Census Bureau: release CB15-113 (June 25, 2015); Vintage 2025 population by single year of age (accessed October 22, 2026).
By Pew Research Center: Silent 1928–1945, Baby Boomers 1946–1964, Gen X 1965–1980, Millennials 1981–1996, and Gen Z from 1997 with no end year.
That is the range the Census Bureau used in its June 2015 release on millennials and boomers. Pew uses 1981–1996. There is no single official definition.
Millennials, at about 73.1 million residents in July 2025 by Pew’s range, ahead of Boomers at about 66.6 million (Census Vintage 2025, birth year approximated as 2025 minus age).
The counts are of people living in the U.S., so they fall as people die: about 75.4 million in the 2015 release and about 66.6 million in 2025 for the same 1946–1964 range.
No. Pew has not defined it or set an end year for Gen Z, and the Census Bureau does not define it either.
Pew’s ranges run 16 to 19 years, and Pew says a typical generation spans 15 to 18 years.