Your age is more interesting than the round number on your birthday cake. Here is how to calculate it precisely.
Most of the time, your age is just "however many candles fit on the cake." But there are moments — driving licences, voter registration, pension eligibility, insurance pricing, even medical dosing — where the exact number of years, months and days actually matters. Calculating it correctly takes more care than you might think.
Age, properly counted, is the number of complete years between your date of birth and today. The two common quirks:
1. Birthday timing. If today is your birthday, you turn that age. If your birthday is later this year, you are still last year's age. 2. Leap days. People born on 29 February only get a "real" birthday every four years; legally they age every 28 February or 1 March depending on jurisdiction.
1. Subtract birth year from current year. 2. If the current month is before your birth month, subtract 1. 3. If the current month equals your birth month *and* today's date is before your birth date, subtract 1.
Example: born 15 August 1990, today 5 June 2026. 2026 − 1990 = 36. June is before August, so subtract 1 → 35 years old.
A 30-year-old has been alive for roughly:
Earth has carried you roughly 28 billion km around the sun in that time. Statistically you have spent about a third of those 30 years asleep — roughly 10 years.
Legal: voting rights, alcohol purchase, marriage, driving, retirement benefits — every threshold needs precise age.
Medical: pediatric drug doses are often calculated per kilo of body weight per year of age; misjudging age by even a year can affect dosing. Vaccine schedules are tied to exact ages in months.
Financial: life-insurance premiums step up every birthday. Retirement-account contribution limits change at certain ages (e.g. catch-up contributions). Pension start dates depend on age in years and months.
Education: school grade placement is often determined by age cut-off dates that vary by country.
Leap years add a 29th day every February if the year is divisible by 4 (with exceptions for century years not divisible by 400). For most calculations the difference is negligible, but over decades it adds up — a 60-year-old has lived through 15 leap days, an extra 360 hours of life that someone born on 1 March missed.
If you were born on 29 February:
Most of the world uses the Western system — age 0 at birth, +1 every birthday. But:
When booking flights, signing contracts or filing immigration paperwork, always use Western reckoning unless explicitly asked otherwise.
Can age be calculated in months? Yes — total months between two dates, common in pediatric medicine ("7 months old").
How do I calculate age between two non-today dates? Use the same method, swapping "today" for the target date.
Does timezone affect age? Only on your birthday — and only if you obsess over the hour.
Use our free Age Calculator to see your age in years, months, days, hours and even seconds — and to count down to your next birthday.