Age Calculator
Work out an exact age in years, months, and days from any date of birth - plus total days lived and the countdown to the next birthday.
Age Calculator
Defaults to today. Change it to find an age at any past or future date.
Age
36yrs 2mo 18d
Total days
13,228
Total weeks
1,889
Total months
434
Total hours
317,472
Birthday details
- Day of the week born
- Friday
- Next birthday
- Jun 15, 2027
- Days until then
- 286
Months are counted by advancing whole calendar months from the birth date, so a 31st-of-the-month birthday lands correctly in February and leap days are counted where they actually occur.
How the age calculation works
Calculating an age sounds trivial and turns out to be one of the more error-prone things in everyday arithmetic, because months are not a fixed length and years are not either.
The correct method works from the largest unit down. Start with the difference in years, then check whether the birthday has actually happened yet this year. If it has not, subtract one year and count the months and days from the most recent monthly anniversary of the birth date.
A worked example. Someone born 15 June 1990, evaluated on 1 September 2025:
- From 15 June 1990 to 15 June 2025 is 35 full years.
- From 15 June 2025 to 15 August 2025 is 2 full months.
- From 15 August 2025 to 1 September 2025 is 17 days.
So the age is 35 years, 2 months, and 17 days — or 12,862 days in total.
The naive approach fails in two specific ways, and both are worth knowing because they show up in real software constantly:
- Subtracting date fields leaves negatives. Take 31 January to 1 March. Subtracting gives 2 months and −30 days, and the usual fix — "borrow the days in the previous month" — borrows February's 28 and still leaves −2. The correct answer is 1 month and 1 day, and getting there requires advancing month by month rather than subtracting fields. This calculator uses the advancing method.
- Assuming 30-day months or 365-day years. Both drift. Between 1 January 2024 and 1 January 2025 there are 366 days because 2024 was a leap year.
Leap years follow a rule with two exceptions: a year is a leap year if divisible by 4, unless it is divisible by 100, unless it is also divisible by 400. So 2000 was a leap year and 1900 was not. Anyone born on 29 February has a birthday only every four years; most jurisdictions treat 1 March as the legal birthday in common years, which is the convention used here for the next-birthday countdown.
Enter a birth date above to see the exact age, the total days lived, the day of the week of the birth, and how long until the next birthday.
Frequently asked questions
How do I calculate my exact age?
Count the complete years from your birth date to today, then the complete months since that anniversary, then the remaining days. Counting forward this way avoids the negative-day problem that comes from subtracting date fields directly.
How many days old am I?
Count the total calendar days between your birth date and today, including every leap day along the way. Someone who has lived 35 years will have passed through roughly nine leap days, so the total is about 12,780 days rather than 35 times 365.
What happens with a February 29 birthday?
A leap-day birthday only falls on the calendar every four years. Most jurisdictions treat 1 March as the legal birthday in common years, which is the convention used here, though some use 28 February. The age in years advances every year regardless.
Which years are leap years?
A year is a leap year if it divides by 4, except that century years must also divide by 400. So 2024 is a leap year, 2000 was one, and 1900 was not. The rule keeps the calendar aligned with the solar year, which is about 365.2422 days.
Can I calculate an age at a past or future date?
Yes. Change the "age at" date to any date you like, to work out how old someone was at an event or will be on a future one. If you set a date before the birth date, the calculator says so instead of showing a negative age.
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