Age Calculator
Calculate exact age in years, months, and days from a date of birth.
Given a date of birth, this tool works out your exact age in years, months, and days as of today (or any other date you choose) — accounting for leap years and the varying length of months, which a naive subtraction gets wrong.
It's handy for eligibility checks, forms that want an exact age rather than just a birth year, or just settling an argument about how many days old someone is.
Why day counts rarely match a quick estimate
- A year is not 365 days. Over any span longer than four years leap days add up — someone who is 40 has lived through about 10 of them.
- Months have no fixed length. 'One month after January 31st' has no obvious answer; the convention used here, and by most calendar software, is to land on the last valid day of the following month.
- Age in years is a floor, not a rounding. You are 39 until the instant of your 40th birthday, even at 39 years and 364 days.
- Different countries count age differently. East Asian age reckoning traditionally counts you as one at birth; this tool uses the international convention of completed years.
Where an exact age is actually needed
Visa applications, insurance underwriting, school admission cut-offs, pension eligibility and legal age thresholds are all assessed on a specific date, which is often not today. Set the 'as of' date to the relevant deadline rather than mentally adjusting from today's age — that adjustment is where mistakes creep in, especially for a birthday falling close to the cut-off.
Frequently asked questions
- Why does my age in days not match a simple day count?
- The calculator accounts for leap years automatically, so the day count reflects the real calendar rather than a flat 365-day year.
- Can I calculate age as of a future or past date?
- Yes — set the 'as of' date to any date you like, past or future, to see age at that point in time.
- Does time zone affect the result?
- The calculation uses calendar dates only, so it's unaffected by time zone — the same dates always give the same answer.
- How is someone born on 29 February handled?
- In non-leap years their birthday is treated as 1 March for the purpose of completed years, which is the common legal convention in most jurisdictions.
- Can I use this to find a date of birth from an age?
- Indirectly — set the 'as of' date and adjust the birth date until the age matches. The calculator works forward from a birth date rather than solving backwards.