Age Calculator
Calculators & Converters
Calculate exact age in years, months, and days from any date of birth. Includes total days lived, the day of the week you were born, and a countdown to your next birthday.
Runs entirely in your browserAbout Age Calculator
The Age Calculator answers the questions 'how old is someone exactly' more precisely than mental arithmetic can. Beyond the obvious year count, it gives you months and days remaining after the year, the exact total of days lived (useful for actuarial-style trivia or 'I'm 10,000 days old' moments), the weekday of your birth, and how long until your next birthday — handy for planning or curiosity.
All dates are interpreted in your local time zone. Calculations use `date-fns` for correct handling of leap years, month-length variations, and edge cases (was someone born on Feb 29 in a non-leap year? Their birthday counts as Mar 1 on those years). You can change the 'as of' date to compute age at any historical or future point — useful for retirement planning, legal age verification, or working out how old someone was at a specific event.
How to use
- 1
Enter the date of birth
Use the Date of birth date picker.
- 2
(Optional) Change the reference date
By default the 'As of' field is set to today. Change it to compute age at any historical or future date.
- 3
Read the breakdown
Three cards show Years (with months and days remainder), Total days lived (with day of the week born), and Next birthday (days remaining and exact date).
- 4
Use today
Click 'Use today' to reset the As of field if you've been exploring historical dates.
Examples
Age from a 1990 birthday to today
Returns full age with year/month/day breakdown.
Output
Born 1990-06-15 → 34 years, 11 months, 4 days (today)Frequently asked questions
How is the year/month/day breakdown computed?+
First subtract whole years. Then advance the date by those years and subtract whole months from there. Then subtract days from there. This gives the 'plain English' breakdown that matches how people naturally say ages.
Why does the day of the week matter?+
Mostly curiosity, but it's also handy for trivia, birth registers, and some cultural traditions. The day of the week is computed deterministically from the date using the Gregorian calendar.
What about ages before 1582 (Gregorian calendar reform)?+
We use the proleptic Gregorian calendar for all dates, which extends the Gregorian rules backward in time. Historians may prefer Julian dates for events before 1582; the difference grows the further back you go.
How does it handle Feb 29 birthdays?+
On non-leap years, the calendar treats the birthday as Mar 1 for 'next birthday' calculations. Total days are exact regardless.
Is my birth date sent anywhere?+
No. All math runs in your browser.
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