Age Calculator
Calculate exact age in years, months and days from a date of birth, plus total weeks, days, hours and the next birthday countdown.
Inputs
Leave blank to use today
Formula
- Age = (Y₂ − Y₁) years, (M₂ − M₁) months, (D₂ − D₁) days (with borrow adjustment)
- Total days = ⌊(t₂ − t₁) / 86 400 000⌋
Calendar age is not a simple day count divided by 365.25 — months have unequal lengths and leap years shift the boundary. The correct method subtracts the calendar components (year, month, day) and borrows from the previous month when the day component is negative, exactly as civil registries do.
Step-by-step calculation
Reference date
t₂
Fri Jul 31 2026
Date of birth
t₁
Thu Jun 15 1995
Calendar difference
Y/M/D subtraction with borrow
31y 1m 16d
Elapsed days
⌊(t₂ − t₁) / 86 400 000⌋
11,369 days
Worked example
- Date of birth 15 June 1995, evaluated on 31 July 2026.
- Years = 2026 − 1995 = 31; months = 7 − 6 = 1; days = 31 − 15 = 16.
- Age = 31 years, 1 month, 16 days ≈ 11 369 days.
Assumptions
- Dates are handled in the browser's local time zone at 00:00.
- Leap days are counted by the calendar itself, not by an average year length.
Tips
- For legal or insurance use, always state the reference date — age is only defined against one.
- Age 'nearest birthday' (used by some insurers) rounds up when more than six months have passed.
Frequently asked questions
How is age calculated exactly?
By subtracting the day, month and year of birth from the reference date and borrowing days from the previous month when needed. This gives the same result as an official age statement.
Why does dividing days by 365 give a different answer?
Because a year averages 365.2425 days. Over 30+ years the drift is several days, which changes the day component of the answer.
Can I calculate age at a past or future date?
Yes — set the 'Age at the date of' field to any date and the calculator evaluates age at that moment.
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