How to use the age calculator
- Date of birth — the day the person was born.
- Age on this date — leave it on today for current age, or pick another date: the age on a wedding day, on a planned retirement date, or on the cutoff date for school enrollment or a youth sports league.
The headline result is the age the way people say it — years, months and days. Below it you'll find the same span as total months, weeks, days and hours, the date of the next birthday and the day of the week the person was born.
How age is calculated
Age is counted the way birthdays are counted, not by dividing days by 365.25:
- Whole years — the number of birthdays that have passed.
- Whole months — the monthly "anniversaries" of the birth day since the last birthday.
- Days — the days left over from the last monthly anniversary to the target date.
Dividing total days by 365.25 gives a decimal age that is close, but it can be a day off right around a birthday and it can't produce the years-months-days breakdown that forms, school records and pediatric charts ask for.
Worked example
How old is someone born on May 15, 1990 on October 8, 2026?
- Years: the 36th birthday was May 15, 2026 and the 37th hasn't arrived, so 36 years.
- Months: June 15, July 15, August 15 and September 15 have passed; October 15 hasn't, so 4 months.
- Days: from September 15 to October 8 is 15 days left in September plus 8 in October — 23 days.
The age is 36 years, 4 months, 23 days. That's 13,295 days in total (1,899 weeks and 2 days), the person was born on a Tuesday, and the next birthday, May 15, 2027, is 219 days away.
Birthdays on February 29
Leap-day birthdays only appear on the calendar in leap years: years divisible by 4, except century years that aren't divisible by 400. 2000 was a leap year; 1900 and 2100 are not. This calculator counts the birthday on February 28 in common years — the same last-day-of-the-month rule used whenever a month is too short for a date. Under that rule, someone born February 29, 2000 turned 1 on February 28, 2001.
Some laws and organizations use March 1 instead. The two conventions differ by a single day, and only around the birthday in common years; if a legal deadline depends on it, check the rule that applies where you live.
The same rule covers birthdays on the 29th, 30th and 31st: someone born January 31 completes a month on February 28 (or 29), April 30 and so on.
When an exact age matters
- Eligibility cutoffs — school entry, youth sports divisions and age-restricted jobs usually ask for the age on a specific date, which is what the second date field is for.
- Retirement planning — set the date to your planned retirement day to see your age then, and continue with the retirement calculator.
To measure the gap between any two dates rather than an age, use the days between dates calculator.
Frequently asked questions
How do I calculate my age in months?
Multiply your whole years by 12 and add the extra months. At 36 years and 4 months that is 36 × 12 + 4 = 436 months. The calculator shows this as total months.
Does the calculator account for leap years?
Yes. It counts real calendar dates, so every February 29 between the two dates is included in the total days, weeks and hours automatically.
How old will I be on a future date?
Change the second date to the future date you are interested in. The result shows your age on that day and how many days remain until your next birthday after it.
What day of the week was I born?
The "Born on a" row shows it. Weekdays shift by one each year (two after a February 29), which is why your birthday lands on a different weekday from year to year.
Why do some government agencies use a different date for my age?
Some rules follow an old common-law convention under which you reach a new age on the day before your birthday. The U.S. Social Security Administration uses it, which is why people born on the 1st of a month are treated as if born in the previous month for some benefit calculations. This calculator uses the everyday convention: you turn a year older on your birthday.
Last updated: October 8, 2026