How age is calculated
Age in the Western convention counts completed years since birth. You are 29 right up until the moment your 30th birthday arrives, no matter how close it is.
Calculating it precisely means working down through the units rather than dividing days by 365.25. First count whole years between the two dates. If the current month and day are earlier in the year than your birth month and day, subtract one, because that birthday has not happened yet. Then count the whole months since that last birthday, and finally the leftover days.
Leap years and the 29th of February
A leap year has 366 days. The rule is that a year is a leap year if it divides by 4, except century years, which must divide by 400. So 1900 was not a leap year but 2000 was.
People born on 29 February — "leaplings", about one in 1,461 — have no birthday in common years. Most jurisdictions treat 1 March as the legal birthday in non-leap years, though some use 28 February. This calculator uses 1 March, which is the more common convention.
| Decade | Leap years |
|---|---|
| 2020s | 2020, 2024, 2028 |
| 2030s | 2032, 2036 |
| 2040s | 2040, 2044, 2048 |
| 2090s | 2092, 2096 |
| 2100 | Not a leap year — divisible by 100 but not 400 |
Age reckoning around the world
Not every culture counts age the same way. The traditional East Asian system counts a newborn as one year old at birth, and everyone gains a year at Lunar New Year rather than on their birthday. Under it a baby born the day before New Year turns two the next day.
South Korea used this system officially until June 2023, when it standardised on the international method for legal and administrative purposes. This calculator uses the international convention throughout.
Frequently asked questions
How do I calculate my exact age?
Count the whole years from your birth date to today, subtracting one if this year's birthday has not arrived yet. Then count whole months since that birthday, then the remaining days.
The calculator above does this and also converts the result into total months, weeks, days and hours.
How is age calculated for someone born on 29 February?
In leap years the birthday falls on 29 February as normal. In common years, most legal systems treat 1 March as the birthday, which is what this calculator uses.
Some jurisdictions and organisations use 28 February instead. The difference matters only for the single day.
Can I find my age on a past or future date?
Yes. Change the second date field to any date and the result updates. This is useful for eligibility checks — working out whether someone will be 18 by a given deadline, for example.
How many days have I been alive?
The calculator shows this directly. As a rough guide, 10,000 days is about 27 years 4 months, 20,000 days is about 54 years 9 months, and 30,000 days is roughly 82 years 1 month.
What is my age in months?
Total months is shown in the tiles above. It counts completed calendar months, not days divided by 30.44 — so someone born on the 31st is treated correctly in months with fewer days.