The rule that determines full age
Subtract the birth year from the reference year, then subtract one more when the reference month and day come before the birthday. The new age applies on the birthday itself.
For a contract, school date, or future trip, use that date as the reference instead of today.
- Before the birthday: reference year − birth year − 1
- On or after the birthday: reference year − birth year
Example for a birth date of October 15, 2000
On August 28, 2026, the birthday has not occurred, so the full age is 25. On October 15, 2026, the full age becomes 26.
Elapsed years, months, and days can differ from simply dividing total days by 365 because month lengths and leap years vary.
Next birthday and total days lived
The countdown uses the nearest upcoming birthday. If this year's birthday has passed, it uses the birthday in the following year.
Total days use actual calendar dates including leap years. Official eligibility still depends on the reference date and rules of the relevant program.
Checks before relying on the result
A reference date earlier than the birth date is not a valid age calculation. Use the legally registered birth date for official matters.
Insurance, pensions, youth fares, and similar programs may define age eligibility differently, so confirm the provider's rules before making a decision.