Age Calculator: Exact Age in Years, Months and Days

Calculate your exact age in years, months and days using your date of birth.

An age calculator that helps users determine their exact age in years, months and days from their date of birth.

Working out someone's exact age sounds easy until the dates stop lining up: a birthday that has not happened yet this year, a month with 28 or 31 days, a person born on 29 February. Dividing the number of days by 365 gets all of these wrong sooner or later. This free age calculator uses real calendar dates instead, so the answer comes out in whole years, months and days.

Enter a date of birth, keep today as the reference date or choose another one, and press Calculate age. The tool also checks for impossible dates, and it shows the total days lived and the next birthday. Below it you will find worked examples and a plain explanation of how leap years and end-of-month dates are handled.

Age Calculator

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How to use the age calculator

1. Enter the date of birth. Type the day and the year, and choose the month from the list. Using month names avoids the day/month confusion between date formats.
2. Check the reference date. It starts as today, taken from your device's clock. To find the age on another date, such as a school cut-off date, a future event or a past date, change it. Press Use today's date to go back to today.
3. Press Calculate age. The result shows the age in years, months and days, followed by the weekday of birth, the total days lived, the number of complete months and the next birthday.
4. Copy or reset. Copy result puts the text in your clipboard. Reset clears the date of birth and sets the reference date back to today.

Worked examples

The values below are the results the calculator is designed to give. You can type each one in to check it.

Example 1: a typical birthday

Inputs: date of birth 15 May 1990, reference date 25 October 2026.
Result: 36 years, 5 months, 10 days. The last birthday was on 15 May 2026, five months of anniversaries (15 June to 15 October) have passed since, and 10 more days bring us to 25 October. Total time lived: 13,312 days, which is 1,901 weeks and 5 days. The next birthday is Saturday, 15 May 2027, in 202 days.

Example 2: born on 29 February

Inputs: date of birth 29 February 2000.
Results: on 28 February 2023 the age is 23 years, 0 months, 0 days because this calculator counts the birthday on 28 February in years that are not leap years. On 1 March 2023 it is 23 years, 0 months, 1 day. On 29 February 2024 it is exactly 24 years.

Example 3: a birth date at the end of a month

Inputs: date of birth 31 January 2023.
Results: on 28 February 2023 the age is 0 years, 1 month, 0 days, because February has no 31st and the monthly anniversary falls on the last day of the month. On 1 March 2023 it is 0 years, 1 month, 1 day.

Example 4: age on a future date

Inputs: date of birth 10 September 2015, reference date 1 January 2030.
Result: 14 years, 3 months, 22 days, with 5,227 days lived by then. This is useful for planning, for example to check how old a child will be on a future date. The tool adds a note when the reference date is in the future.

Example 5: why a 365-day shortcut fails

Someone born on 1 January 2000 has lived 8,765 days on 31 December 2023. Dividing by 365 gives about 24.01, which suggests they are already 24. The calendar answer is 23 years, 11 months, 30 days, because six leap days fall in between and their 24th birthday is one day away.

How the calculator works

• Calendar dates, not 365-day years. The calculator never divides days by 365. It counts whole months on the calendar, then whole years from those months, and finally the leftover days.
• Finding the months. It looks for the latest "monthly anniversary" of the birth date that is not after the reference date. Years and months are taken from that, and the days are counted from that anniversary to the reference date.
• Short months. If the birth day does not exist in a month (the 31st in a 30-day month, or the 29th or 30th in February), the anniversary falls on the last day of that month. That is why 31 January plus one month is 28 February, or 29 February in a leap year.
• Leap years. A year is a leap year when it is divisible by 4, except for century years, which must also be divisible by 400. So 2000 and 2024 were leap years, while 1900 and 2100 are not. A date such as 29 February 2023 is rejected as impossible.
• Born on 29 February. In years that are not leap years, the birthday is counted on 28 February. Some countries and legal systems use 1 March instead, so the result can differ by one day on those two dates.
• Total days. Total days, weeks and weekdays come from exact day numbers on the calendar, so time zones and daylight saving do not affect them.

For a short explanation of the leap-year rules, NASA Glenn Research Center's K-12 calendar notes cover why only some century years are leap years.

Limitations and common mistakes

• Whole days only. The tool does not use the time of birth or time zones, so it cannot tell you the age in hours or at an exact moment.
• Gregorian calendar only. Dates must be in 1583 or later, and are treated as Gregorian dates. Countries adopted this calendar at different times, so for very old dates the result may not match local historical records.
• Not a legal tool. Rules for legal age, school entry, retirement or eligibility can vary by country and may count differently, especially for 29 February birthdays. For official purposes, check the rules of the authority concerned.
• Different calculators, different days. Two correct tools can differ by a few days for end-of-month birth dates, because there is no single universal convention. This page explains the one it uses.
• Check the reference date. If the result looks wrong, make sure the reference date is the one you intended. It is filled from your device's clock, which may be wrong.
• Future dates. A birth date later than the reference date is rejected. A reference date in the future is allowed and is flagged as a projection.

Frequently asked questions

How does the calculator treat leap years?

It uses the Gregorian rule: a year divisible by 4 is a leap year, except century years that are not divisible by 400. A date like 29 February is accepted only in leap years.

What happens if I was born on 29 February?

In years that are not leap years, the calculator counts your birthday on 28 February, and it adds a note under the result. On 1 March the age is one day past the birthday.

Why is my age in days not simply my years times 365?

Because leap years add an extra day about every four years. The total days shown are counted exactly on the calendar, so they include every leap day.

Can I find the age on a past or future date?

Yes. Change the reference date. A future reference date is allowed, and the result is shown as the age on that date.

Why do I get an error for some dates?

The calculator checks that the date exists, for example that 31 April or 29 February 2023 are rejected, and that the date of birth is not after the reference date. The message tells you which field to fix.

Does the tool store my date of birth?

No. The calculation runs in your browser, and the tool does not send, save or log the dates you enter. As with any page on this site, the page itself may load ads or analytics described in our Privacy Policy.

Conclusion

Use real calendar dates, check the reference date, and remember that end-of-month and leap-day birthdays depend on a convention, which this page states openly. For more free tools, try our Percentage and Discount Calculator or the Secure Password Generator.