How age is counted
Age in years is how many birthdays have happened on or before the chosen date. Months and leftover days are counted from the last birthday-month. Leap-day birthdays are treated as February 28 in common years.
Worked example
Born 19 September 1990, on 19 September 2026 you turn 36 years 0 months 0 days. The day before, you are 35 years 11 months 30 days or 31 days depending on the month length.
Age in whole years is what most forms want. This page also shows leftover months and days. Time zones follow the browser clock, not the hospital’s.
Common questions
Why do some sites differ by one day?
Time zones and whether they count today. This page uses local calendar dates only.
Can I use it for a pet or a company?
Yes. Any start date works.