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About this tool
Calculates age based on birthdate
The Age Calculator turns a date of birth into an exact age using native JavaScript Date arithmetic — no date library and no server call. Calendar years, months and days are computed by borrowing the real length of the previous month (28, 29, 30 or 31 days, so leap days resolve correctly), while total weeks, days, hours, minutes and seconds come from the raw millisecond difference between your birth moment and now. A one-second interval re-runs the whole calculation while the page is open, so the seconds lived and the next-birthday countdown tick live on screen.
Open Age Calculator on AltFTool — it loads instantly in your browser.
Enter your date of birth, and optionally your time of birth, in the fields at the top.
Press Calculate Age to see exact years, months and days plus total weeks, days, hours, minutes and seconds.
Scroll for your next-birthday countdown, day milestones, birth-date facts, and a side-by-side age comparison with someone else.
Days and months are worked out against the actual length of each calendar month, so a birth date late in a long month doesn't drift the way fixed 30-day arithmetic does, and leap days are counted.
The calculation re-runs every second while the page is open, so seconds lived, total hours and the countdown to your next birthday update as you watch.
The calculation makes no network requests, has no upload step and writes nothing to local storage — your date of birth stays in page memory and disappears when you close the tab.
No signup and no cap on how many dates you calculate. Results can be copied as text, copied as a link, shared, or sent to your browser's print dialog to save as PDF.
Enter your date of birth and press Calculate Age. The result shows exact calendar years, months and days, plus totals for weeks, days, hours, minutes and seconds lived. The time-of-birth field is optional — adding it makes the hour, minute and second figures exact instead of counted from midnight.
The calculator answers directly: total days is the millisecond gap between your birth moment and right now divided by 86,400,000 and rounded down. It's shown next to your 1,000-, 5,000-, 10,000- and 25,000-day milestones, each with the calendar date it falls (or fell) on, plus the date you'd reach 100 years.
Yes. Ages come from native JavaScript Date arithmetic rather than a flat 365-day year, so every 29 February between your birth date and today is counted. When the day figure needs to borrow, it borrows the true length of the preceding calendar month — 28, 29, 30 or 31 days.
Usually rounding. Many calculators divide total days by 30 for months or 365 for years, which drifts by several days. This one reads years, months and days from the calendar itself and reports the raw totals separately, so it won't always match a rounded estimate.
No. Everything runs in your browser in JavaScript — there's no upload, no API call and no localStorage write. The date exists only in the page's memory for the session.
Yes. Leave the time field blank and the count starts at 00:00 on your birth date in your device's local time zone; fill it in and the hours, minutes and seconds lived become exact, with the next-birthday countdown aligned to the hour you were born.
The countdown shows days, hours, minutes and seconds remaining, the weekday the birthday falls on, and the age you'll turn. If this year's birthday has already passed, it rolls to next year's date automatically.
It derives your Western zodiac sign and its associated colour, your Chinese zodiac animal from the 12-year cycle anchored to 1900, your generation label (Greatest Generation through Gen Beta), and the traditional birthstone and birth flower for your birth month. Heartbeat and breath counts are illustrative figures based on average rates of 72 beats and 16 breaths per minute — estimates, not measurements.