Age calculator

Enter a date of birth to get an exact age in completed years, months, and days, on today or on any later date. The page also gives total months, weeks, and days, the weekday you were born, and the next birthday. Counting is truncated, never rounded up.

How old are you

How we counted

Age is truncated, never rounded up. You are not 37 the day before your 37th birthday, and a person born today has lived 0 days, not 1.
We count by walking forward from the birth date: whole years first, then whole months, then the leftover days. The common shortcut of subtracting the parts and borrowing once can return a negative day count, and does on 31 January 1990 measured at 1 March 2026.
Month arithmetic uses constrain overflow, the same rule as the date calculator: January 31 plus one month is February 28 or 29, not March 2 or 3.
A 29 February birth date has no anniversary in a common year, so one has to be chosen. We default to March 1, with a toggle to February 28. Other tools choose differently and some cite the common legal position in parts of the Commonwealth for February 28. We disclose the choice rather than hide it, and we do not claim ours is the legally correct one.
There is no "include end date" toggle. The days between dates calculator has one because contract counting needs it. A toggle that can make someone a day older is a defect.
Other calculators answer the same question differently. For a birth date of 31 March 1990 measured at 28 February 2026, two we tested return 35 years, 10 months and 28 days where we return 35 years, 11 months and 0 days. The difference is the month rule above: we treat 31 March to 28 February as a whole month, because February has no 31st.
This block is the only part of the page that works without JavaScript. The calculator itself needs it, so with scripting turned off you get these rules and no controls. Some other age calculators do the arithmetic on the server and work either way.

This is a calendar calculation. Where an exact age decides a legal right, a benefit or an eligibility date, the rule that applies is set by your jurisdiction and may differ from the convention shown here.

Where these rules come from

Month arithmetic, constrain overflow. Our own rule, set on 19 August 2026, and the same one the date calculator applies.
The leap-day default of March 1, with a February 28 toggle. Our own choice, matching the control already live on the date calculator.
A leapling reaches an age at the start of 1 March in a common year. UK Family Law Reform Act 1969, section 9(1). This is one jurisdiction and we do not present it as universal.
The February 28 position. Taken by calculatgeek.com, which calls it the Commonwealth position. That is a competitor's assertion, not an authority, and we name it as one.

Measured on this page, in this browser

Requests: · from Resource Timing
Script: · KB of a 100 KB budget

Everything here runs in your browser. We never send the dates of birth you enter to ourselves or anywhere else. It stays on your device. Once the page has loaded, you can disconnect and keep working. How we build tools

February 29 birthdays

Someone born on 29 February has a real anniversary only once every four years, and in the other three the calendar simply has no such date. Every age calculator has to pick a substitute, and the pick changes the answer.

This page defaults to March 1 and offers February 28. The control appears only when the birth date you entered is 29 February, because for everyone else it does nothing at all.

The choice reaches further than it looks. For a 29 February birth date it changes the displayed age on 29 consecutive days, from 28 February through 28 March, and it changes the total month count on 28 February only. For the next birthday the rule is exact: the two settings differ on precisely those dates whose next anniversary falls in a common year. In a leap year both settings name 29 February, so both agree.

One consequence catches people out. A leapling's next anniversary can fall in an earlier month than the last one, because the following year may be a leap year. Asked on 2 March 2027 under the March 1 setting, the next birthday is 29 February 2028, not 1 March 2028.

Age on a date that is not today

The second field takes any date on or after the birth date, so you can ask how old someone was at a past event or will be at a future one. Every figure on the page answers that same hypothetical, including the next birthday, which is counted from the date you entered rather than from the real today.

The as-of date cannot be earlier than the birth date. Nobody has a negative age, and returning zero instead would be a wrong answer wearing the costume of a right one.

Questions

Why does this disagree with another age calculator?

Almost always the leap-day rule or the month-end rule. Ask both tools for the age of someone born on 31 January measured at 1 March: the answer depends on whether January 31 plus one month is February 28 or March 3. We publish both rules above; many tools publish neither.

Is the day I was born counted?

Total days counts from the birth date up to but not including the as-of date, so a person born today has lived 0 days. The same convention runs through every figure here.

Does it handle dates before 1900?

Yes, and the century rule matters there: 1900 was not a leap year, though 2000 was. Someone born on 29 February 1896 waited eight years for a true anniversary.

Does anything leave my browser?

No. The dates stay in the tab. A share link carries them after the hash mark, which browsers do not transmit to a server, so the link reconstructs the dates on the recipient's machine without passing through ours.

Related tools

To move a date by an amount rather than measure between two, use the date calculator, which shares this page's counting rules. For a plain span with an inclusive option, use days between dates. More at the date and time hub.

Maintained by Aaron Wilson
Published August 28, 2026. Last updated August 28, 2026. Method and formula: how we build tools. Something wrong? Tell us and it goes in the changelog.