Guide
How to Calculate Your Exact Age in Years, Months, and Days
"How old are you?" seems simple until you need the exact answer — for a form, a legal document, or a milestone. Calculating age precisely means handling months of different lengths and leap years, which is where hand calculations go wrong.
The basic method: subtract the dates
Start with the year: subtract your birth year from the current year. If your birthday hasn't happened yet this year, subtract one more. Born in June 1990 and it's now March? You're 35, not 36.
For the full answer in years, months, and days, subtract each part separately — months from months, days from days — borrowing when the top number is smaller, exactly like column subtraction in school.
Borrowing months and days
Say today is March 5, 2026, and you were born on August 22, 1998. Days: 5 − 22 doesn't work, so borrow a month. The month before March is February, which has 28 days in 2026, so 5 + 28 = 33, and 33 − 22 = 11 days.
Months: you borrowed one, so it's 2 − 8, which also doesn't work. Borrow a year (12 months): 2 + 12 = 14, and 14 − 8 = 6 months. Years: you borrowed one, so 2025 − 1998 = 27 years. Final answer: 27 years, 6 months, 11 days.
The leap year trap
When you borrow a month, the number of days you add depends on which month you borrowed — 28, 29, 30, or 31. February has 29 days in leap years (years divisible by 4, except century years unless divisible by 400 — 2000 was a leap year, 1900 was not).
This is the step where manual calculations most often go wrong. The calculator handles month lengths and leap years automatically, which is why it's the safer option for anything official.
Age in total days, weeks, or months
Sometimes you need age in a single unit: a baby is "14 weeks old," a milestone is "10,000 days." Converting years to days means multiplying by 365 and then adding back one day for every leap year that passed — easy to get wrong by a few days over decades.
Fun fact: your 10,000th day alive happens around age 27 years and 4 months. Many people celebrate it as a milestone birthday most of us miss.
Age on a future or past date
The same subtraction method works between any two dates, not just birthday-to-today. To find your age at a future event — "how old will I be when I retire in 2040?" — subtract your birth date from that date instead of today's.
The calculator accepts any end date, so you can answer questions like how old you'll be at a wedding, a graduation, or when a loan is paid off.
Try it yourself
Put this guide into practice with our free Age Calculator — no sign-up, no download.
Open the Age Calculator