About one in every 1,461 people — roughly 5 million worldwide — is born on February 29. They are called "leaplings," and they share a curious problem: their birthday only appears on the calendar every four years. In the other three years, when exactly do they turn a year older? The answer involves a mix of math, law, and tradition.

Why leap day exists at all

Earth takes about 365.2422 days to orbit the Sun — not a clean 365. Without correction, calendars would drift away from the seasons over time. Adding a day every four years corrects most of the drift. Skipping the leap day on years divisible by 100 (but not 400) handles the rest. So 2024 was a leap year. 2100 will not be. 2000 was.

How often leap days actually occur

A leap day occurs:

  • Every year divisible by 4 (2024, 2028, 2032, ...)
  • Except years divisible by 100 (1900, 2100 — no leap day)
  • Unless also divisible by 400 (2000 — leap day returns)

The result: exactly 97 leap days every 400 years, or one every 4.12 years on average.

The legal question: when do leaplings age up?

In the United States, there is no single national rule; the answer depends on the state and on the law involved. The two common conventions are:

  • February 28. The day before March 1.
  • March 1. The "next" calendar day after February 29 would be.

For most practical purposes — driving age, voting age, age-of-majority, legal drinking age — the effective birthday in non-leap years is February 28 or March 1, depending on the law that applies. A leapling born Feb 29, 2004 turned 18 in 2022 on one of those two dates. When it matters, check with the agency involved, such as the DMV or the election office.

Other countries set their own rules, usually in the law that defines when a person reaches a given age, and they do not all pick the same day. If a date matters legally, check the rule where you live.

The cultural question: when do leaplings celebrate?

Celebration is personal, not legal. Common choices:

  • February 28 — the last day of February, closest to "the day before March."
  • March 1 — the first day of March, the calendar-neighbor approach.
  • Both days — two parties are better than one.
  • February 29 only — celebrating just every four years (the minimalist approach).

Age in years: the math

For a leapling born February 29, 2000, their age on April 21, 2026:

  • Birthdays "celebrated": 2001, 2002, 2003, 2004 (actual leap), 2005 ... 2024, 2025, 2026. Simple year difference: 26 − 0 = 26.
  • As of April 21, the date is past both Feb 28 and March 1, so the latest birthday has occurred.
  • Age: 26 years.

A leapling born in 2000 has an actual Feb 29 birthday in 2004, 2008, 2012, 2016, 2020 and 2024 — that is 6 "real" birthdays in their first 26 years, with the next one in 2028, at age 28. Hence the joke "I'm only 6 leap years old."

Edge case: newborns born Feb 29

A baby born Feb 29, 2024 turns 1 on Feb 28, 2025 or March 1, 2025 by most conventions. Their actual 1st "leap-day" birthday is Feb 29, 2028 — when they are 4 years old on the calendar.

Leap year milestones to know

  • Most recent: 2024 (Feb 29, 2024 occurred)
  • Next: 2028 (Feb 29, 2028)
  • Following: 2032, 2036, 2040...
  • Skipped: 2100 (divisible by 100 but not 400)
  • Restored: 2400 (divisible by 400)

No one will be born on February 29, 2100: 2100 is not a leap year, so the date will not exist.

Why this matters beyond parties

Legal contracts, insurance renewals, driver's license expiration dates, subscription anniversaries, warranty periods, and birthday-triggered benefits all touch the leap-day edge case. Most software handles it by defaulting to February 28 or March 1 in non-leap years, but inconsistent handling across systems can cause confusion. When specifying important dates, use ordinal rules ("60 months from contract date") rather than calendar dates when leaplings are involved.

Calculate around a leap day

Our age calculator accepts February 29 birth dates. In non-leap years it counts the birthday as March 1: for someone born February 29, 2000, it shows 24 years, 11 months, 30 days on February 28, 2025, and exactly 25 years on March 1, 2025. It also gives the age in total months, weeks and days, and the number of days until the next birthday. If you know a leapling, enter their birth date and see how the dates fall. The math is quirky — the math is also fun.