“How old am I exactly?” sounds trivial until you try to do it by hand and the months don't line up. Calculating an exact age means subtracting one date from another and borrowing across months and years — the same care a stopwatch takes. Here's the method, plus a free age calculator that gives years, months and days in one click.
The manual method
Subtract the date of birth from today, one unit at a time — days, then months, then years:
- Subtract the day numbers. If today's day is smaller, borrow the days from the previous month and reduce the month count by one.
- Subtract the month numbers. If that goes negative, borrow 12 months from the year and reduce the year count by one.
- Subtract the year numbers. What's left is the exact age.
Worked example
Born 15 August 1998, today 3 July 2026:
- Days: 3 − 15 is negative, so borrow → 3 + 30 − 15 = 18 days, carry −1 month.
- Months: 7 − 8 − 1 = −2, so borrow 12 → 10 + 7 − 8 − 1 = 10 months, carry −1 year.
- Years: 2026 − 1998 − 1 = 27 years.
Exact age: 27 years, 10 months, 18 days.
The leap-year gotcha
Borrowing “days from the previous month” means the number of days varies — 28, 29, 30 or 31 — so a hand calculation is easy to get slightly wrong, especially around February in a leap year. Someone born on 29 February only gets a “true” birthday every four years, and different systems treat their non-leap-year birthday as 28 Feb or 1 March. A calculator handles all of this consistently.
Where exact age matters
Eligibility cut-offs (school admission, retirement, visas), precise milestones, and working out the gap between two people's ages all need exactness, not just “27”. To count the days or working days between any two dates instead, use the date calculator.
FAQ
How do I calculate age from a date of birth? Subtract the birth date from today, borrowing across months and years as needed.
What about a 29 February birthday? In non-leap years it's usually observed on 28 Feb or 1 March, depending on the system.
Can I find the age difference between two people? Yes — subtract the two birth dates the same way.
Is my data private? Yes — the calculator runs in your browser and stores nothing.