Age Calculator

Calculating your exact age sounds like it should be simple subtraction, but doing it by hand is more fiddly than it looks, since months and years don't all have the same number of days. This calculator handles that arithmetic for you, comparing your date of birth to today (or any other date you choose) and breaking the difference down into complete years, months, and days.

The trick is borrowing correctly when the day-of-month or month doesn't divide evenly, the same way you'd borrow when subtracting by hand. If you were born on the 20th and today is the 5th, you can't have a negative number of days, so the calculator borrows a full month's worth of days from the month column, using however many days that particular month actually has. The same borrowing happens between months and years when needed. It's exactly the kind of careful, error-prone bookkeeping a calculator is good at and a person doing mental math often gets slightly wrong.

Total days lived is a simpler figure: just the raw number of days between your birth date and the reference date, useful for anything from "golden birthday" celebrations (turning an age that matches your birth date) to curiosity about a big round-number milestone like your 10,000th day alive.

Days until your next birthday looks ahead instead of back, finding the next occurrence of your birth month and day from the reference date and counting forward. If that date has already passed this year, it automatically looks to next year instead, so the count is never negative.

You can also change the "as of" date to something other than today, which is useful for figuring out how old you were (or will be) on a specific date in the past or future, like a wedding, graduation, or anniversary.