Age Calculator

How Age Calculator Works

This calculator works out your exact age -- in years, months, and days -- between a date of birth and any "as of" date you choose (defaulting to today), and also reports totals like days and weeks lived and a countdown to your next birthday.

Formula & Method

The age is built up calendar-style, not by dividing total days: years, months, and days are found by subtracting the birth date's year, month, and day from the "as of" date's year, month, and day. If the day subtraction goes negative, one month is borrowed and the number of days in the previous calendar month is added back; if the month subtraction then goes negative, one year is borrowed and 12 months are added back. This mirrors how people naturally describe age ("36 years, 1 month, 19 days") and correctly accounts for varying month lengths. Total days, weeks, and months lived are then computed as straight differences between the two dates, and the next birthday is the nearest upcoming date matching the birth month and day.

Worked Example

For a date of birth of June 15, 1990, measured as of August 3, 2026, this calculator reports an exact age of 36 years, 1 month, 19 days -- with 13,198 total days lived, 1,885 total weeks lived, 433 total months lived, and 316 days remaining until the next birthday.

Frequently Asked Questions

Why is my age in years different from simply subtracting birth year from current year?

Subtracting years alone ignores whether your birthday has already happened this year. This calculator instead does a full calendar subtraction of year, month, and day, so the year count only increases once the birth month and day have actually passed in the "as of" date.

How are days handled across months of different lengths?

When the "as of" day of the month is earlier than the birth day of the month, the calculator borrows a month and adds the number of days in the previous calendar month (28, 29, 30, or 31, depending on the month and leap years) -- so the day count always reflects the actual calendar, not a fixed 30-day assumption.

Can I calculate my age as of a past or future date instead of today?

Yes -- the "Age As Of" field defaults to today's date but can be changed to any date, letting you find out how old you were on a specific past date, or how old you will be on a specific future date.

What happens if the date of birth is after the "as of" date?

The calculator shows a message asking you to check the dates instead of a result, since age can't be computed when the birth date falls after the date you're measuring from.