Age Calculator
Enter a birth date to get exact age in years, months, and days, total days lived, and days until the next birthday.
| Total days lived | |
|---|---|
| Total months | |
| Total weeks | |
| Days until next birthday |
How to use this tool
Enter a birth date. The "as of" date defaults to today but can be changed to calculate age at any past or future date. Select "Calculate age" to see the full breakdown.
About this calculation
Age is calculated the way a calendar would: whole years since the birth date, then whole months since the most recent birthday, then remaining days — not a simple division of total days by 365.25, which can be off by a day in either direction depending on leap years.
All date math uses UTC internally to avoid timezone-related off-by-one errors.
Frequently asked questions
How is age in years, months, and days calculated?
It's a calendar-aware difference, not a simple division of total days. Years, months, and days are counted the way people actually count age: whole years since the birth date, then whole months since the last birthday, then remaining days — matching how a calendar would show your age.
What happens with a February 29 birthday in a non-leap year?
This tool follows the common convention of treating March 1 as the equivalent date in non-leap years (rather than February 28), consistent with how JavaScript's date handling normalizes February 29 in a non-leap year.
Can I calculate age as of a date other than today?
Yes. Set the "as of" date to any date to see the age (or time between two dates) at that point — useful for calculating age at a past or future event.