Age Calculator
Enter a date of birth to get the exact age in years, months and days, plus the total months, weeks and days lived, the weekday of birth and the date of the next birthday. Change the second date to find the age on any day, past or future.
Today by default. Change it to find the age on another day.
Age
Enter a date of birth to see the age.
The calculation runs in this browser tab. Nothing you enter is uploaded, saved or logged.
How is age defined and counted?
Age is the time between a person’s date of birth and a reference date, usually today. In everyday life it is given in completed years, but forms for infants, school cut-off dates and medical records often need months and days as well.
A calendar age counts whole years first, then whole months, then the days that remain. Because months last between 28 and 31 days, a calendar age cannot be turned into a number of days by a fixed factor, so this calculator also reports the exact number of days between the two dates.
How to use the Age Calculator
- Enter the date of birth. You can type it or use the date picker of your browser.
- The age is measured on today’s date by default. To measure it on another day, such as a future deadline, a school cut-off or a past event, change the “Age on” date.
- Read the age in years, months and days, and the totals and birthday details below it.
- Use Copy result to copy the age as text, or Reset to clear the birth date and return the second date to today.
Formula
- Completed months
- m = the largest whole number such that (birth date + m months) ≤ age-on date
- Years and months
- years = ⌊m ÷ 12⌋ and months = m mod 12
- Days
- days = age-on date − (birth date + m months)
- Total days
- total days = day number(age-on date) − day number(birth date)
- Weeks
- weeks = ⌊total days ÷ 7⌋, with total days mod 7 days left over
When a month is added to a date, the day of the month is kept if it exists. If it does not (31 January + 1 month, or 29 February + 1 year), the last day of that month is used. Someone born on 31 January therefore completes one month on 28 or 29 February.
Other age calculators subtract the day, month and year fields one by one and borrow days from the previous month. That can give a different number of days when the birth day is the 29th, 30th or 31st; both methods agree on the years and on the total number of days.
Worked example
Someone born on 15 March 1990, with the age measured on 20 June 2024. These are the results the calculator gives:
| Question | Result |
|---|---|
| Age | 34 years, 3 months, 5 days |
| Completed months | 411 |
| Total days lived | 12,516 |
| Total weeks | 1,788 weeks and 0 days |
| Born on a | Thursday |
| Next birthday | Saturday, 15 March 2025 (turning 35, in 268 days) |
Assumptions and limits
- Only the calendar date is used. The time of birth and time zones are ignored, so a result can differ by a day from a calculation that includes them.
- Born on 29 February: in years that are not leap years, the birthday is counted on 28 February. Laws differ on whether the legal birthday falls on 28 February or 1 March in those years, so check the rule that applies to you for legal purposes.
- All dates use the Gregorian calendar, extended backwards before its introduction (1582 in some countries, much later in others). Ages computed from very old dates may differ from historical records. Years 1 to 9999 are supported.
- “Today” comes from your device’s clock and time zone. If your clock is wrong, so is the default date.
- This is a calculation aid, not proof of age. Do not use it as a legal or official age check.
Frequently asked questions
How is age calculated in years, months and days?
The calculator finds how many whole months have passed since the date of birth. Dividing by 12 gives the years and the remainder is the months. The days are those left between that last monthly anniversary and the age-on date. From 15 March 1990 to 20 June 2024 that is 34 years, 3 months and 5 days.
Why does another calculator show different days for the same dates?
Methods differ for birth dates on the 29th, 30th or 31st. This calculator adds whole months to the birth date and uses the last day of a shorter month where needed; other tools subtract field by field and borrow days from the previous month. The years and the total number of days are the same either way.
How is a 29 February birthday handled?
In leap years the birthday is 29 February. In other years it is counted on 28 February, both for the age and for the next birthday date. Some countries treat 1 March as the legal birthday in those years, so check the local rule if the exact day matters legally.
Can I find the age on a future or past date?
Yes. Change the “Age on” date to any day from the year 1 to 9999. This is handy for school entry cut-offs, retirement dates, competitions and anniversaries. The date of birth must not be after the age-on date.
How many days old am I?
The “Total days” figure is the number of days between your date of birth and the age-on date, so a baby born yesterday is 1 day old. It comes from exact day numbers in the calendar, so leap days are included correctly.
Does the calculator use my time zone or my time of birth?
Not for the age: it works on calendar dates only. Your device’s date and time zone are used just to fill in today’s date as the default for the second field.
Is my date of birth stored or sent anywhere?
No. The calculation runs in your browser, and the dates stay in the page until you close or reload it or press Reset.