Age Calculator
Calculate your exact age in years, months, and days from any birth date. Also shows your total age in months and days, plus how many days until your next birthday. Accounts for leap years automatically.
Quick answer
Age in years = current year − birth year, minus 1 if your birthday hasn't happened yet this year. The calculator above also gives you exact months and days, total days lived, and countdown to your next birthday.
Age Calculator
How age is calculated
The naive formula is just current year − birth year, but that's only right
if your birthday has already passed this year. The correct approach is to start with the
year difference, then subtract 1 if today's month-and-day is before the birth's
month-and-day. For more precision, the calculator also computes the remaining months and
days by borrowing from the previous month when needed — identical to how you'd subtract
dates by hand.
The total-days figure comes from subtracting the two dates in milliseconds and converting to days. Leap years are handled automatically by JavaScript's Date object: February 29 exists in years divisible by 4, except century years not divisible by 400 (so 1900 was not a leap year, but 2000 was).
When to use it
Age calculators are useful for filling out forms that ask for "age as of a specific date" (school enrollment, sports eligibility, insurance applications), for figuring out how old someone was in a historical photo, for planning an age-themed birthday surprise, or for knowing exactly how many days you've been alive. Some people check their "days until next birthday" as a way to gamify the countdown.
Common mistakes
- Just subtracting birth year from current year. A person born in December 1990 is not 35 in January 2026 — they're still 35 only after their December birthday.
- Forgetting timezones. If you were born in one timezone and the calculator runs in another, the "exact days" count can be off by one. The effect is tiny and mostly doesn't matter.
- Using a 30-day month for calculations. Months have 28, 29, 30, or 31 days. The calculator handles the variation; by-hand math often doesn't.
Frequently asked questions
How do you calculate exact age?
Subtract the birth year from the current year, then adjust by whether the birthday has passed this year. For exact years, months, and days, borrow days from the previous month when today's date is less than the birth date.
How old am I in days?
Enter your birth date above. The calculator shows your total age in days, factoring in leap years. A 30-year-old is roughly 10,957 days old.
Does age calculation account for leap years?
Yes. The calculator uses JavaScript's native Date object, which handles leap years automatically.
How is age determined in different countries?
Most countries use the Western system: you turn N on your birthday. Traditional Korean age starts at 1 and everyone ages on New Year's Day. This calculator uses the Western system.