Check your age today or on another calendar date
Enter a Gregorian birth date to calculate completed years of age. The reference date starts as today on your device, but you can choose another date to check an age in the past or future. The results also show the difference between birth and reference years, traditional Korean counting age, days elapsed since birth, and the next birthday. These measures use different conventions, so read the label beside each number. For a leap-day birth, this calculator increases completed age on March 1 in a non-leap year. This is the calculator's stated convention, rather than a universal claim about legal age rules.
Step-by-step instructions and example screen
From input to result
- Enter the Gregorian birth date.
- Keep today's reference date or select another date to compare.
- Calculate and read the completed age, comparison measures, and next birthday separately.
When to use this tool
Check today's completed age
Enter the birth date and keep the default reference date. The calculator determines whether this year's birthday has already arrived.
Compare a particular date
Change the reference date to inspect completed age on that day. Compare the birthday's eve with the birthday to see the change.
Plan for the next birthday
Read the next birthday date and days remaining. On the birthday itself, the remaining count is zero.
Examples and calculation method
Worked examples
| Birth date | Reference date | Completed age |
|---|---|---|
| 2000-10-23 | 2026-10-22 | 25, before the birthday |
| 2000-10-23 | 2026-10-23 | 26, on the birthday |
| 2000-02-29 | 2026-03-01 | 26, using this calculator's leap-day convention |
Completed birthdays and the leap-day convention
Subtract the birth year from the reference year, then subtract one more if that year's birthday has not arrived. The birthday itself starts the new completed year. Year-based age is the year difference alone; traditional Korean counting age adds one. For February 29 births, the calculator uses March 1 in a non-leap year for both age changes and the next birthday. Input dates must be valid, with birth no later than the reference.
Understanding your result
- Select the age measure actually requested by the form or service; the displayed measures are not interchangeable.
- Use Gregorian dates and check that the reference date is not earlier than the birth date.
- February 29 is treated as March 1 in non-leap years by this calculator; check specific eligibility rules separately when they matter.
Frequently asked questions
Frequently asked questions
Why are several different ages displayed?
Completed age reflects birthdays. Year-based age subtracts birth year from reference year, while traditional Korean counting age adds one. They describe different counting conventions.
What happens for a February 29 birthday?
This calculator increases completed age on March 1 in non-leap years and uses the same convention for the next birthday. Specific institutions or jurisdictions can require their own rules.
Can I enter a lunar-calendar birthday?
Convert it to the Gregorian birth date first. This calculator does not convert lunar-calendar dates.
What age is shown on the date of birth?
Completed age is zero and elapsed days are zero. Traditional Korean counting age displays one under its separate counting convention.