Health
Age Calculator
Find your exact age — or anyone's — down to the day. Enter a date of birth and see age in years, months, and days, total days lived, and how long until the next birthday.
Your age
31
Exact age
31y 1m 4d
Total days lived
11,357
Next birthday in
331 days
Age is calculated the standard way: you turn a year older on each birthday, and months/days count the time since the last one.
How it works
Age is calculated the way people actually count it: you turn one year older on each birthday. The months figure counts full calendar months since your last birthday, and days count what's left after that.
Because calendar months have different lengths, the day count borrows from the actual previous month when needed — the same way you'd do subtraction by hand. This handles leap years and 28/30/31-day months correctly.
Total days lived is a straight difference between the two dates, which is why it's exact even when the years/months/days breakdown involves uneven month lengths.
age_years = asOf.year − birth.year (minus 1 if birthday not yet reached)
age_months = calendar months since last birthday
age_days = days since last monthly anniversary
total_days = (asOf − birth) / 86,400,000 msFrequently asked questions
How is exact age calculated?
Start with the difference in years, then subtract one if this year's birthday hasn't happened yet. Months count the full calendar months since the last birthday, and days count the remainder — borrowing from the previous month's actual length when needed.
How does the calculator handle leap-year birthdays (February 29)?
The total-days count is always exact because it works with real calendar dates. For year counting, someone born February 29 is treated as turning a year older on March 1 in non-leap years, matching common legal convention.
Can I calculate age at a date other than today?
Yes — change the 'age as of' field to any date. This is handy for forms that ask your age on a specific date, like exam eligibility or retirement paperwork.
Why do some countries count age differently?
Most of the world uses the international system this calculator uses: you're 0 at birth and gain a year each birthday. Korea historically used a system where you're 1 at birth and everyone ages on New Year's Day, though the international system became standard there in 2023.
How many days old is a 25-year-old?
Roughly 9,131 days — 25 years × 365.25 average days per year. The exact figure depends on how many leap days fall inside the particular 25-year span.