How to calculate your exact age in years, months and days
Count forward from the date of birth: first the whole years up to the last birthday, then the whole months after it, then the days that are left. Someone born on August 15, 1990 is 36 years, 1 month and 20 days old on October 5, 2026. Thirty-six years take you to August 15, 2026, one month to September 15, and 20 more days to October 5.
Step by step
- Years. Subtract the birth year from the current year: 2026 − 1990 = 36. If this year's birthday hasn't come yet, subtract 1. August 15 has passed, so the answer is 36.
- Months. Starting from the last birthday (August 15, 2026), count how many times you've passed the 15th. September 15 is one; October 15 hasn't come yet. That's 1 month.
- Days. Count from the last of those dates (September 15) to today: 20 days.
Birthdays at the end of a month
Step 2 needs a rule for months that are too short. When the monthly date doesn't exist, Daycount uses the last day of that month, the same rule it uses for adding months to a date. For someone born on January 31, 2000, the monthly date in February 2026 is February 28, so on March 1, 2026 they are 26 years, 1 month and 1 day old.
A common shortcut subtracts the years, months and days separately and "borrows" the length of the previous month when the days go negative. It breaks on a date like this: 1 − 31 + 28 (the days in February 2026) is still negative. Counting forward from the birthday avoids the problem.
Born on February 29
In years without a February 29, Daycount treats February 28 as the birthday. A person born on February 29, 2000 is 25 on February 27, 2026 and turns 26 on February 28, 2026. Other rules may use March 1 instead, so for anything official, such as a license or a benefit that starts at a certain age, check the rule that applies.
Age in days, weeks or months
The same person, counted up to October 5, 2026:
| Unit | Born Aug 15, 1990 |
|---|---|
| Days | 13,200 days |
| Weeks | 1,885 weeks and 5 days |
| Months | 433 full months |
| Next birthday | Aug 15, 2027, in 314 days |
The day count is a plain subtraction, so the day of birth is day 0. A 10,000-days-old celebration falls 10,000 days after the birth date, which for this example was Sunday, December 31, 2017. The guide to counting days between dates explains when to add 1.
The other rows in the calculator
Below the main result, the age calculator also shows two ways of counting age that are used in Korea: the year age (this year minus the birth year) and the traditional Korean age, which starts at 1 and goes up every January 1. You can ignore them unless you need them.