How old are you, exactly?

How is age calculated?

Count the full years since the birth date, then the full months since the last birthday, then the days left over. Someone born on May 15, 1990 is, on September 26, 2026, 36 years, 4 months and 11 days old: 36 years to May 15, 2026, four months to September 15, and 11 more days.

How many days old am I?

Count the days between your birth date and today. For a May 15, 1990 birthday, on September 26, 2026 that is 13,283 days — 36 years of 365 days, 9 leap days (1992 through 2024) and 134 days since the last birthday.

How do I find my age on a specific date?

Change the "Age on" date. It starts at today, but you can pick any date, past or future — for example the date of an application or a retirement date.

What if I was born on February 29?

In years without a February 29, this calculator counts the birthday on February 28. Some people celebrate on March 1 instead, and state laws differ on which day you legally turn a year older, so check if it matters for a document.

What day of the week was I born?

The result shows it. May 15, 1990, for example, was a Tuesday. The calculator uses the Gregorian calendar, which the United States has used since 1752.

Why do two age calculators sometimes disagree by a day?

Months have different lengths, so "one month after January 31" has no single answer, and tools differ in whether they count the starting day. This calculator counts whole years first, then whole months since the last birthday, then the remaining days, which is the way people state their age.

How do I figure out how many weeks old someone is?

Count the total days between the two dates and divide by 7, ignoring the remainder. A baby that is 100 days old is 14 weeks and 2 days old.

Does the time of birth or the time zone matter?

Only for the exact hours. The calculator works with calendar dates, so the age changes at midnight on the birthday and the answer does not depend on the hour of birth. Someone born late at night who is now in a different time zone may see a different local date than the one on the birth certificate.

How the calculation works

The calculator subtracts the birth date from the "age on" date in three steps. It counts the full years until the most recent birthday, then the full months after that birthday, and finally the days that are left. If the day of the month has not yet been reached, one month is borrowed. Total days come from the difference between the two calendar dates, so leap days are included automatically; total weeks are the total days divided by seven, rounded down. The weekday of birth follows from the calendar and the next birthday from the date's month and day.

Worked example

Someone was born on March 12, 1985. On October 27, 2026 the full years are 41 (the birthday this year, March 12, has passed), then 7 full months from March 12 to October 12, and 15 more days to October 27. So the age is 41 years, 7 months and 15 days. Counted in days, the difference between the two dates is 15,204 days, which is 2,172 complete weeks. The next birthday, March 12, 2027, is 136 days away.

Common mistakes

• Counting years by subtraction only. 2026 − 1985 = 41 is right here, but someone born in December would be one year younger on October 27. The birthday has to be reached first.
• Treating every month as 30 days. A quick estimate of "years × 12 + months" is fine, but days must be counted on the real calendar, where months run from 28 to 31 days.
• Forgetting February 29. People born on a leap day need a rule for non-leap years; this tool uses February 28. For a legal document, check which rule applies.

Sources and related calculators

Method: standard Gregorian calendar arithmetic. Related: date calculator, day of the week calculator and adjusted age calculator.