Age Calculator — years, months and days

How to use

What it's for

Work out exactly how old someone is — in years, months and days — today or on any other date, such as the day of an exam or an application deadline.

Before you start

Have the person's date of birth. If a form sets an age limit on a particular day, have that date to hand too.

Enter the date of birth
In Date of birth, pick the day the person was born from the calendar, or type it in. The page starts with a sample date, so replace it with the real one.
Choose the day to measure to
Age at starts as today. Leave it for someone's age right now, or change it to see how old they were, or will be, on another day — handy when a rule says "not over 35 on the closing date".
Press Calculate
Press Calculate. The answer already changes as you pick the dates; the button brings it into view, which helps on a phone where it may have scrolled away.
Check the working
Under Calculation, the age is laid out step by step: the years, the months, the days, then the totals and the days left until the next birthday.

Reading the result

Age: the big number is the age in whole years. Under it is the exact age in years, months and days.
Total months and Total days: the same age counted all in months, or all in days.
Next birthday: the date of the next birthday and how many days away it is — the "d" means days. On the birthday itself it reads Birthday and Today instead.

If it goes wrong

An error says the date is before the date of birth: Age at is earlier than the birthday. Check the year in both boxes.
Enter a date. appears: one of the two boxes was cleared. Pick a date in it again.
The months and days look one off near the end of a month: months have different lengths, so one month after 31 January is 28 February. The page counts whole months first, then the days left over, which is how people count.

What this is

Age in years, months and days, counted the way a person counts: whole months are advanced from the date of birth for as long as that stays on or before the second date, and whatever is left over is the days.

That matters at month ends. One month after 31 January is 28 February, so 1 March is one month and one day later — not one month and two. Subtracting the numbers and borrowing once gives a negative day count and a wrong answer.

Questions

How is someone born on 29 February aged in a normal year?

Their birthday is counted as 28 February. Rolling it forward to 1 March would mean a leap-day baby reaches eighteen a day later than everyone born the same week, which is not how age of majority is read.

Why can I change the second date?

So you can work out age at any date, not just today — how old someone was on a particular day, or will be at a future one. It defaults to today for the common case.

Why do the months and days look odd near month ends?

Because months are different lengths. One month after 31 January is 28 February, so 1 March is "1 month and 1 day" later, not "1 month and 2 days". The calculation advances whole months first and counts the leftover days, which is how people count.

How it counts

31 Jan → 1 Mar

Advance one month 28 Feb

Days left over 1

Every date here is compared as text in YYYY-MM-DD form and every step is integer arithmetic on the parts. No timezone can move a birthday by a day.

Calculation