Age calculator
Runs entirely in your browser. Your files and data never leave your device.
| Age | 30 years, 0 months, 0 days | |
|---|---|---|
| Total months | 360 | |
| Total weeks | 1,565 | |
| Total days | 10,957 | |
| Total hours | 262,968 | |
| Next birthday | Thursday, October 1, 2026 | |
| Days until next birthday | 0 | |
| Day of the week you were born | Tuesday | |
| Next 1,000-day milestone | 11,000 days · Friday, November 13, 2026 |
About this tool
Type a birth date and this tool works out an exact age: years, months, and days, along with totals in months, weeks, days, and hours. It also shows the next birthday, what day of the week it falls on, and how many days are left until it arrives. You can change the “as of” date to check an age at any point in time, not just today.
Is my data uploaded anywhere?
No. The calculation happens entirely in your browser, so it’s fine to use this for someone else’s birth date, a document deadline, or any other date you’d rather not put through a server.
How does it handle a leap day birthday?
A birth date of February 29 has no exact anniversary in a non-leap year. This calculator marks the birthday on March 1 in that case, following the common convention that a leap-day birthday “arrives” the day after February ends, rather than moving it back to February 28. The same rule applies to the age breakdown itself: when it counts whole months and days, a February 29 anniversary in a non-leap year lands on March 1 too, so the numbers stay consistent with the birthday countdown.
How does the year/month/day breakdown work?
The tool counts the largest whole number of calendar months between the birth date and the “as of” date, then works out the leftover days from there. It anchors each monthly step to the calendar, so a birth date of January 31 advances to February 28 (or 29 in a leap year) rather than spilling over into March, the way naive day-counting math sometimes does. That anchoring also avoids a subtler bug: a single fixed correction for month length can occasionally undercount by miscalculating both the month and the day, whereas recomputing each month boundary directly cannot. The totals (months, weeks, days, hours) are plain day counts converted to each unit, not derived from the years/months/days breakdown, so they stay accurate independent of how the breakdown rounds.
If you set an “as of” date earlier than the birth date, the tool reports an error instead of showing a negative age.
Common uses: figuring out someone’s exact age for a form, checking how many days are left until a birthday or anniversary, or working out an age as of a specific past or future date. See the Wikipedia article on leap years for background on why some February 29 birthdays get tricky, and MDN’s Date reference for how JavaScript represents dates under the hood.