How to Calculate Your Exact Age (Leap Years Included)
Subtracting birth year from current year gets you close and is wrong about half the time. Here is the method that gives an exact age in years, months and days — and the leap-year detail that trips up spreadsheets.
Unless also divisible by 400 → leap year after all.
So 1900 was not a leap year, but 2000 was. Between 1 January 2000 and today there have been 7 leap days (2000, 2004, 2008, 2012, 2016, 2020, 2024).
Multiplying 26 years by 365 gives 9,490 days — six days short of the real 9,724 even before the partial year is counted. Any age-in-days figure that ignores leap days is wrong.
Converting to other units
Unit
How to get it
Example (9,724 days)
Weeks
days ÷ 7
1,389 weeks, 1 day
Hours
days × 24
233,376 hours
Months (approx)
years × 12 + months
319 months
Why "months" is always approximate: calendar months run from 28 to 31 days, so there is no fixed number of days in a month. Any tool converting a large day count into months is using an average — which is why the exact years-months-days form is the one to trust.
The 29 February question
Roughly one person in 1,461 is born on a leap day. In common years the date simply does not exist, so legal systems pick a substitute — most commonly 1 March, though some use 28 February. Driving licences, pensions and insurance policies may not agree with each other, which is worth checking if a birthday falls on the boundary of an age-based entitlement.
If you need the gap between two arbitrary dates rather than an age, or you are converting shift lengths for payroll, the decimal-hours conversion handles the smaller units.
Subtract the birth year from the current year, then check whether this year's birthday has already passed. If it has not, subtract one. For months and days, work down from years to months to days, borrowing from the previous month when the day count goes negative.
How many days old am I?
Count the total days between your birth date and today, including one extra day for every leap year in between. Someone born on 1 January 2000 has lived 9,724 days as of 16 August 2026 — about 1,389 weeks, including 7 leap days.
When do people born on 29 February celebrate?
Legally it varies. Most jurisdictions treat 1 March as the date a leap-day birthday takes legal effect in common years, though some use 28 February. Socially, people pick whichever they prefer. In a leap year the date exists and the question disappears.
Why does multiplying years by 365 give the wrong answer?
It ignores leap days. Over 26 years there are typically six or seven of them, so the shortcut undercounts by about a week. It also ignores the partial year since your last birthday.
How is age counted differently around the world?
Most countries use the international system, where you turn one on your first birthday. Traditional East Asian age reckoning counted a baby as one at birth, adding a year each Lunar New Year — South Korea formally moved to the international system in 2023 for most purposes.
