How age is counted
In most of the world — including every country that follows the Gregorian calendar — age is counted from the birth date and increments on each birthday. If you were born on April 4, 1990, you turn one on April 4, 1991, and every April 4 afterward. The age calculator on this page mirrors that convention exactly: it counts complete years first, then the leftover months, then the leftover days.
Some East Asian systems traditionally use a different convention where a newborn is considered one year old and everyone ages together on Lunar New Year. Legal, medical, and administrative systems worldwide have moved to the international standard, and that's what this calculator implements.
Worked example
Born April 4, 1990, today July 17, 2026. Step one: complete years. From April 4, 1990 to April 4, 2026 is 36 years. Step two: complete months from the last birthday. April 4, 2026 to July 4, 2026 is 3 months. Step three: leftover days. July 4 to July 17 is 13 days. Answer: 36 years, 3 months, and 13 days. The total is also 13,253 days, or about 1,908 weeks.
Leap years and end-of-month edge cases
A year is a leap year if it's divisible by 4, except years divisible by 100 that aren't divisible by 400. That's why 2000 was a leap year but 1900 wasn't. This calculator uses the JavaScript Date object, which correctly implements the full Gregorian leap-year rule, so February 29 birthdays are handled cleanly: on non-leap years, the birthday is treated as March 1 for legal purposes, but this tool reports the exact interval either way.
When you need an exact age
- Legal thresholds: driving, voting, and drinking ages depend on the exact date, not a rough estimate.
- Insurance and pension paperwork typically require age at a specific policy date.
- School and sports eligibility use a cutoff date; a few days can decide the class or age group.
- Medical dosing for pediatric patients often uses age in months for children under three.
- Immigration forms sometimes need age at the date of application, not today.
Age calculator vs. date-difference calculator
This calculator is optimized for the common case where one of the two dates is a birth date and you want the result expressed in years, months, and days. If you want the interval between any two arbitrary dates — a project deadline, an anniversary, a countdown — the dedicated date difference calculator is a better fit and can also show the result in weeks, business days, or hours.
| Unit | Value |
|---|---|
| Years | 36 |
| Years + months + days | 36y 3m 13d |
| Total months | 435 |
| Total weeks | 1,893 |
| Total days | 13,253 |
How to use this age calculator
- Enter your date of birth (year, month, day).
- Leave the target date on today for your current age, or set a future date to see how old you'll be.
- Read the exact answer in years, months, and days plus totals in weeks, months, and days.
Privacy
The calculation runs entirely in your browser. Your birth date is never sent to a server or stored — clear the fields and the value is gone. The same applies to every other calculator on this site.