Age calculator and days between dates

An exact age, or the days between two dates

This page does two jobs. The “Age” tab is an age calculator: enter a date of birth and it gives the age in years, months and days, the weekday of the birth and the time left until the next birthday. The “Between two dates” tab is a date difference calculator: it counts the days, weeks, months and working days in a period, and adds or subtracts days from a date.

Use it for a baby's age in months, for the age reached on a school cut-off date, on the day of a driving test or at retirement, to count down to a holiday, a wedding or an exam, or to measure a notice period, a contract, a hire period, a delivery window or length of service.

How to use it

1. Age. Fill in “Date of birth”. “Reference date” starts on today's date: change it to get the age on any other day. “Reference: today” resets it.
2. Between two dates. Fill in “Start date” and “End date”. If the end comes before the start, the tool puts the two dates in order and says so.
3. Tick “Include the last day” to count the end date as well, as you would for a car hire.
4. “Shortcuts”: “Start: today”, “End: today”, “End: + 30 days”, “End: + 90 days” and “End: end of year”.
5. Under “Add or subtract days from a date”, pick a date, “Add” or “Subtract”, a number and a unit (days, weeks or months). The resulting date is written out in full.
6. “Copy link” gives an address that reopens the page with your dates: #a=1990-05-17 or #d=2026-01-01&f=2026-12-25.

How a length of time is counted

Months last 28, 29, 30 or 31 days, so the tool counts whole months first, from one day of the month to the same day of a later month, then the days left over. If that day does not exist in the final month, the last day of the month is used: 31 January 2025 to 28 February 2025 is 1 month, which is 28 days.

From 1 January 2026 to 25 December 2026 there are 11 months and 24 days. That is 358 days, or 51 weeks and 1 day, 256 of them between Monday and Friday. A child born on 5 June 2010 is 16 years, 2 months and 27 days old on 1 September 2026.

Leap years. A year has 365 days, or 366 in a leap year. A year is a leap year if it divides by 4, except century years, which must divide by 400: 2000 and 2024 are leap years, 1900 and 2100 are not. From 1 January to 31 December 2024 there are 365 days, and 366 with “Include the last day” ticked.

Born on 29 February. In other years, this tool counts the birthday on 28 February. Born on 29 February 2000, you turn 25 on 28 February 2025.

Calendar days, working days, business days. Working days, or business days in the United States, usually mean Monday to Friday without public holidays. The tool counts Monday to Friday only. It knows no bank or federal holidays: subtract them yourself.

A point of reference. 10,000 days is roughly 27 years and four and a half months. Born on 17 May 1990, you reached it on 2 October 2017.

Frequently asked questions

Why do two calculators differ by one day?

From Monday 2 March to Monday 9 March 2026 there are 7 days and 5 working days if the 9th is left out, and 8 days and 6 working days if it is counted. The “Include the last day” box switches between the two conventions.

Do time of birth and time zone matter?

No. The calculation uses calendar dates only. Neither daylight saving time nor time zones shift the result.

What day of the week was I born on?

The “Day of birth” line gives the weekday. Try 1 January 2000: it was a Saturday.

Are my dates stored?

No. They stay in your browser and in the page address after the # sign, a part that browsers do not send to the site.