Age Calculator

How to use Age

Enter the date of birth. Read the age in completed years, plus the months and days on top. Check the total in days if you want the number that sounds impressive at parties. Enter a second date instead of today to find someone's age as of a specific day — a policy start, an exam date, a photograph.

Why age is measured in completed years

Age counts what has finished, not what is in progress. Someone eleven months past their birthday is not "nearly the next age" for any official purpose — they are still the previous one, and will be until the day itself. Every form, ticket price and eligibility rule works this way, which is why the honest answer is years plus a remainder rather than a rounded figure.

That remainder is where the interesting part lives. For a child it is the difference between two developmental stages. For a legal threshold it is the difference between yes and not yet. Rounding an age up is a courtesy at a birthday party and a problem on a form.

The 29 February question

People born on a leap day get a real birthday roughly once every four years, and the years in between are settled by convention rather than arithmetic. Two conventions are in circulation: 28 February — treat the birthday as the last day of the same month. Common in legal contexts, since it means the age advances within the correct month.

1 March — treat it as the day after the full 28-day February. Preferred by those who like their birthday to fall after a complete February. Neither is wrong, but they differ by a day, and in a year where a threshold falls in that gap the difference is not academic. If the age matters formally, check which convention applies where you are.

Ages other than your own

The same calculation answers a lot of questions that are not about people: how old a document is, how long a company has existed, how far apart two people are in age, how old someone was on a given historical date. For an age gap, run both birth dates and compare — the gap in days holds steady, while the gap in years appears to change between birthdays.