Age Calculator

How age is calculated

Your age in years is the number of birthdays you have had. The months and days are counted from the last birthday:

1. Years. Born May 15, 1990: by October 7, 2026 the 36th birthday has passed, so the age is 36.
2. Months. From May 15, 2026, whole months fit up to September 15: 4 months.
3. Days. From September 15 to October 7: 22 days.

The result is 36 years, 4 months, 22 days. The totals use the plain difference between the dates: 13,294 days, or 1,899 weeks and 1 day, or 436 months and 22 days. Hours are the days times 24, since a date of birth has no time of day; for an age in hours to the minute, add the time you were born with the time duration calculator.

When a month is shorter than the birth day — born on the 31st — the monthly anniversary falls on the last day of that month: from January 31, one month on is February 28. That is how calendars, contracts and spreadsheets move by whole months, and it is why January 31, 2000 to March 1, 2026 is 26 years, 1 month and 1 day.

Why calculators disagree by a day

Most differences come from borrowing days. Subtracting October 7 from May 15 field by field gives “−8 days”, so a calculator has to borrow a month’s worth of days. Borrowing from the month before today (September, 30 days) gives 22 days, the same answer as counting from September 15. Borrowing from the birth month (May, 31 days) gives 23, which is what calculator.net showed when we ran it on October 7, 2026. Both agree on the total of 13,294 days; only the split into months and days differs. This calculator counts forward from the last monthly anniversary, so the months and days always add back up to the date you entered.

Born on February 29

People born on leap day have a calendar birthday only once every four years — 2024, 2028, 2032 — under the Gregorian rule that skips leap years in century years not divisible by 400. In other years the birthday has to be placed on February 28 or March 1. This calculator uses March 1: on February 28, 2026, someone born February 29, 2004 is 21 years, 11 months and 27 days old and turns 22 the next day. The total of 8,035 days is the same either way. For a legal age — a driver’s license, a contract, retirement benefits — the rule is set by the law or agency involved, so check it if a single day matters.

Age on a past or future date

Many rules ask for an age on a fixed date rather than today: a school entry cutoff such as “5 years old by September 1”, a youth sports age group “as of December 31”, travel insurance quoted by age at departure, or the age at which a benefit starts. Enter that date in Age on to see the exact age then, and whether a birthday falls before it. To find the date a certain number of days or years from a birthday — the 10,000th day, for example — use the date calculator; to count the days between any two dates, the days between dates calculator.

Babies and young children

For babies, age in weeks and months is more useful than years: the result shows the age in months and days and in weeks and days, so 8 months and 22 days is also 37 weeks and 6 days. Pediatric growth charts, feeding guides and developmental milestones are usually given in months until about age two, then in years and months. For a due date or gestational age, use a tool made for pregnancy, which counts from the first day of the last period rather than from birth.

Milestone ages in the U.S.

To see the date you reach one of these ages, enter your date of birth and move Age on until the years change, or add the years to your birthday with the date calculator. The Social Security Administration treats people born on the 1st of a month as if born the month before, so check its own table for a benefit date.

Your next birthday and the day you were born

The result also gives the weekday you were born on and the date and weekday of your next birthday, with the number of days to go. A birthday moves forward one weekday each year, or two after a February 29, so a birthday on a Wednesday in 2026 falls on a Thursday in 2027. For today’s date and week number, see what is today’s date.

Generations by birth year

These are the ranges Pew Research Center uses. Other researchers draw the lines a year or two apart, and there is no agreed end year for Generation Z, so the calculator names a generation only for these years.

Calculating age in a spreadsheet

In Excel or Google Sheets, with the date of birth in A1, =DATEDIF(A1,TODAY(),"Y") returns the full years and =DATEDIF(A1,TODAY(),"YM") the months since the last birthday. Microsoft notes that the "MD" option can give wrong results, so compute the days as =TODAY()-EDATE(A1,12*Y+M), where Y and M are the years and months from the first two formulas. =TODAY()-A1 gives the age in days.