Age Calculator
Calculate age based on date of birth and an optional comparison date.
Enter birth date to calculate age.
What This Calculator Does
"How old am I, exactly?" has a more precise answer than just a single number of years — this tool breaks it down into years, months, and days, calculated from a birth date and either today's date or any other date you choose to check against. It's the same underlying math whether you're figuring out your own age or someone else's age on a specific past or future date.
How to Use It
Enter a Date of Birth — the field won't accept a date in the future. The "Age at Date" field is optional and defaults to today, but you can set it to any other date to see how old someone was, or will be, at that point instead. The result reads back as a full sentence: years, months, and days, all three spelled out together rather than just a single rounded figure.
The Formula
This calculator uses date-fns's intervalToDuration function, which breaks the span between two dates into calendar-aware years, months, and days rather than just dividing a raw day count by 365.25. That distinction matters: calendar months don't all have the same number of days, so a duration expressed this way stays accurate no matter which months the interval happens to cross, including how it handles leap years — a leap day simply becomes one of the days counted in whichever month it falls into, rather than needing any special-case handling.
A Worked Example
Someone born on 2000-01-01, checked against 2024-01-01, is exactly 24 years, 0 months, and 0 days old — a clean whole-number case since both dates share the same month and day. A birthday that doesn't land on a full year works differently: born 2020-01-01, checked against 2020-03-15, comes out to 0 years, 2 months, and 14 days — two full months (January into March) plus 14 additional days. Leap-day birthdays resolve cleanly too: someone born 2000-02-29, checked against 2004-02-29 (both leap years), is exactly 4 years, 0 months, 0 days old, since both dates fall on a real Feb 29 four years apart.
FAQ
- How is age calculated?
- Enter your date of birth and optionally a comparison date. The calculator uses intervalToDuration from date-fns to compute exact years, months, and days.
- Can I calculate age at a past date?
- Yes, use the optional 'Age at Date' field to calculate how old you were or will be on any specific date.