Age calculator
Find an exact age in years, months, and days between any two dates. It works for birthdays, anniversaries, project timelines, or any "how long since" question — and unlike rough estimates, it handles leap years and uneven month lengths correctly.
How to use this calculator
Choose a birth date (or any start date) and an as-of date (which defaults to today). The result breaks the span into full years, then leftover months, then leftover days — the way people naturally state an age. You can also use it for any elapsed-time question, like how long you've been at a job or how many days until a milestone.
How the calculation works
Counting years, months, and days sounds simple but hides some traps, because months have different lengths and some years have a leap day. The reliable method works from the largest unit down: subtract the years first, then the months, then the days, and "borrow" from the next unit up whenever a value goes negative — exactly like long subtraction. When the day count comes up short, the calculator borrows the correct number of days from the previous month (28, 29, 30, or 31 as appropriate), which is why it stays accurate across February and leap years where simpler "divide by 365" approaches drift.
A worked example
Someone born on March 15, 1990, measured as of June 1, 2026, is 36 years old, plus the months and days from March 15 to June 1 — which works out to 2 months and 17 days. So the exact age is 36 years, 2 months, 17 days. A quick "2026 minus 1990 = 36" gets the years right by luck here, but breaks the moment the as-of date falls before the birthday in that year. The full method handles every case.
Why "years only" isn't enough
Plenty of situations need precision beyond whole years: an infant's age in months, eligibility cutoffs measured to the day, or contracts that hinge on an exact anniversary. Estimating age by dividing total days by 365.25 gets close but can be off by a day around leap years. Working in real calendar units avoids that error entirely.
Frequently asked questions
Does it handle leap years correctly?
Yes. Because it borrows the actual number of days in each month rather than assuming a fixed year length, leap days are accounted for automatically. A span crossing February 29 is counted accurately.
Can I calculate a future date span?
Yes — set the "as of" date later than the start date to measure time forward, such as days until a birthday or deadline. The tool measures the gap between any two dates in either direction.
What if the two dates are the same?
The result is zero years, zero months, zero days. If you accidentally set the as-of date before the birth date, the calculator will let you know so you can swap them.