Age Calculator

Calculate exact age in years, months, days, hours, and seconds with milestones & facts.

Include Time of Birth

Date of Birth

Age At Date

How Age Is Calculated

Age is the elapsed time between a birth date and a reference date (defaulting to today). This calculator counts complete years first, then the remaining whole months, then the leftover days — correctly handling months of different lengths and leap years by borrowing from the previous month when needed. It also shows total weeks, hours, minutes, and seconds lived, plus a countdown to your next birthday. All math runs locally in your browser.

Built and maintained by Meet Shah · Last updated 1 August 2026

What this tool is used for

Getting an exact age in years, months and days for a form.
Working out an age at a specific past or future date.
Checking an age against an eligibility threshold.
Calculating a duration since an event rather than a birth.
Confirming an age you calculated by counting.

How it works in practice

A worked example

A date of birth on the last day of a month is being checked in early March, which is the case that used to be reported wrongly.

Input

Date of birth  31 January 2000
Age at date     1 March 2026

Output

EXACT AGE   26 years, 1 month, 1 day
TOTAL DAYS  9,526

One month and one day, because the anniversary of the thirty-first of January does not exist in February and the convention is to treat it as that month's last day. So the count runs from the thirty-first to the twenty-eighth as a whole month, and then one further day to the first of March. The total in days underneath is computed independently, straight from the elapsed milliseconds, which is why it is worth reading as a cross-check on the calendar breakdown rather than as a restatement of it.

The edge case that catches people

That exact case used to print a negative number. The arithmetic subtracts the day-of-month fields and then borrows from the preceding month when the result goes below zero, and borrowing February's twenty-eight days from a deficit of thirty leaves minus two — so the page read one month and minus two days. Swept across 21,670 pairs of dates, the old chain produced a negative component on 150 of them, all of them births on the twenty-ninth, thirtieth or thirty-first. Borrowing the larger of the two values fixes it and cannot go negative.

When not to use this tool

A calendar breakdown is not a single number and cannot be compared like one. The same interval is one year and eleven months or twenty-three months depending only on how you choose to say it, and neither is more correct — so anything that needs to sort, compare or accumulate durations should hold the elapsed days or seconds and format them for display at the very end. The leap-day case is a genuine ambiguity rather than a bug: a birthday on the twenty-ninth of February has no anniversary in three years out of four, and every system picks a side.

Frequently Asked Questions

How is age actually calculated?: By calendar difference, not by dividing days by 365.25. Subtract the years, then decrement if the birthday has not yet occurred this year. The division method drifts by a day or more across a lifetime because of leap years.
When does a 29 February birthday fall in a common year?: Jurisdictions genuinely disagree. Most of the UK and the US treat 1 March as the legal date for coming of age; New Zealand and Taiwan use 28 February. There is no universal answer, which is why software must pick a rule and state it.
Does East Asian age reckoning differ?: Traditionally yes — Korean age counted you as 1 at birth and added a year each New Year, so a December baby could be 2 within weeks. South Korea legally standardised on international age in June 2023, but the traditional count persists socially.
Why do two age calculators disagree by a day?: Almost always timezone handling. If the birth date is parsed as UTC midnight and compared against local time, the result can be off by one either side of the date line. Age arithmetic should use calendar dates, never timestamps.
How is age in months counted?: By whole calendar months elapsed, which is ambiguous at month ends: from 31 January, is 28 February one month? Most implementations clamp to the last valid day, so it counts as one — but the rule should be stated, not assumed.
Why does the legal age of majority not always follow the birthday?: Because some jurisdictions historically treated a person as reaching an age on the day BEFORE the anniversary, a rule still reflected in parts of English and Japanese law. For most purposes the birthday applies, but the exception is real.

Common errors and gotchas

Subtracting years and ignoring whether the birthday has passed, which is off by one for half the year.
Overlooking leap days for a 29 February birth date, which conventions handle differently.
Ignoring time zones, so a date near midnight gives a different age in two places.
Assuming months are equal lengths, which makes a months-and-days result ambiguous.
Using the result for a legal threshold, where the jurisdiction's own rule applies.