Age calculator. Exact to the second.

How to use the Age Calculator

This calculator works out an exact age in years, months and days, counts down to the next birthday, and tells you the weekday someone was born. It uses calendar math, counting whole years, then whole months, then leftover days, so month lengths and leap years are handled correctly. Use it for forms, eligibility checks, birthday planning or comparing two ages.

Step by step

1. 1
   Enter the date of birth

   Pick a date in the Date of birth field. The result appears as soon as the date is valid. Until then the panel asks you to enter one.

2. 2
   Add a birth time if you know it

   Fill in Birth time (optional) to add hours and minutes to the exact age. The next birthday countdown then counts down to that time of day instead of midnight.

3. 3
   Choose the moment to measure to

   Use the current time and keep it ticking live is on by default, so the age and the countdown update every second. Uncheck it to measure to another moment, then set Age as of date and Age as of time, for example a deadline or a past event.

4. 4
   Compare with someone else

   Enter a second date in Compare with a second person (optional). An Age gap box shows that person's exact age, who is older, and the gap in years, months and days plus total days.

5. 5
   Turn on the extras

   Check Show fun lifetime estimates to add heartbeats, breaths, full moons seen, trips around the Sun and hours asleep.

6. 6
   Copy the result

   Press Copy summary to put a plain text summary on your clipboard: the as of date, birth date, exact age, totals, next birthday and the age gap if you entered one.

Reading the result

• Exact age is the calendar age. Born March 15, 1990 and measured on October 14, 2026, it reads 36 years, 6 months, 29 days, because the day count borrows the 30 days of September.
• Born on a shows the weekday of the birth date. The totals beside it count whole months, weeks, days and hours lived so far.
• Next birthday shows days, hours, minutes and seconds left, the age that will be reached and the weekday it falls on. On the birthday itself it says Today.
• Someone born on February 29 has the birthday counted as March 1 in years that are not leap years.
• The fun estimates assume about 72 heartbeats and 16 breaths a minute, 8 hours of sleep a night and a lunar cycle of 29.53 days. They are rough averages, not medical data.

Tips and common mistakes

• If the panel says the date of birth is after the as of moment, check the year in both date fields. The tool will not count backward.
• To find the age on a fixed date, such as an exam cutoff, uncheck the live option first. While it is checked the as of fields are locked and the age is measured to the current time.
• When you uncheck the live option, the as of fields keep the date and time from when the page loaded or the option was last checked, so set them to the moment you want. If you clear Age as of date, the tool measures to the current time.
• The second person has no time field, so their age is measured from midnight on their birth date.

Privacy and limits

All the math runs in your browser. The dates are not uploaded, not saved and not remembered after you close the tab. The copied summary goes only to your own clipboard.

Back to the tool

Every number a birthday hides.

Frequently asked questions.

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