Age Calculator

An age calculator counts whole years first, then whole months, then the days left over. Someone born on March 15, 1991 is 35 years, 7 months and 17 days old on November 1, 2026: the 35th birthday was March 15, 2026, seven month marks later is October 15, and 17 more days reach November 1. That is 13,015 days in total.

How to use the age calculator

1. Pick a tab: Exact age, Next birthday, Age gap between two people, Birth year for a quick answer, or Baby & child.
2. Enter the date of birth. The “age on” date starts at today, read from your device. Change it to find an age on any past or future date, such as a school cut-off or a retirement date.
3. Read the answer in years, months and days. Under it you get total months, weeks, days, hours, minutes and seconds, the weekday of birth and a countdown to the next birthday.
4. Open Show steps to see the count worked out for your dates. Copy result puts the answer on your clipboard.

For a February 29 birthday, a small switch appears so you can count the birthday on February 28 or March 1 in common years.

How to calculate age in years, months and days

Age is counted in three passes, from the largest unit to the smallest:

1. Whole years: find the last birthday on or before the date. The number of that birthday is the age in years.
2. Whole months: step forward from that birthday one month at a time, keeping the same day number, until one more step would pass the date.
3. Days: count the days from the last month mark to the date.

For the example above, the last birthday before November 1, 2026 was March 15, 2026, the 35th. Month marks run April 15, May 15, and so on to October 15, which is 7 months. From October 15 to November 1 is 16 days left in October plus 1 in November, so 17 days. The age is 35 years, 7 months and 17 days.

The totals come from the day count. From March 15, 1991 to November 1, 2026 is 13,015 days. Divide by 7 to get 1,859 weeks and 2 days. In months it is 12 × 35 + 7 = 427 months and 17 days. Hours are 13,015 × 24 = 312,360, assuming birth at midnight.

Worked example: age difference between two people

Person 1 was born on September 2, 1988 and Person 2 on March 15, 1991. The age gap is Person 1’s age on the day Person 2 was born. Two birthdays take Person 1 to September 2, 1990. Six month marks reach March 2, 1991, and 13 more days reach March 15. The gap is 2 years, 6 months and 13 days, or 924 days (exactly 132 weeks). In whole years the gap is 3 between Person 1’s birthday in September and Person 2’s in March, and 2 for the rest of the year.

Month ends: why some age calculators disagree

Months have 28 to 31 days, so a day number such as the 31st does not exist in every month. This calculator uses the month-end rule: when the birth day number is missing, that month is complete on the month’s last day.

Take a birth date of January 31, 1990. On March 1, 2026 the last birthday was January 31, 2026 (age 36). February 2026 has no 31st, so the first month mark is February 28. One more day reaches March 1. The age is 36 years, 1 month and 1 day.

Calculators that “borrow 30 days” or divide days by an average month length can give a different day count near month ends. The total number of days never changes, so check that figure when two tools disagree.

Leap-day birthdays: February 29

A year is a leap year when it divides evenly by 4, except century years, which must divide evenly by 400. So 2000 and 2024 were leap years, but 2100 will not be. Someone born on February 29 has a real birthday only in leap years.

In the other years, people pick one of two days, and laws and agencies differ by country. This calculator counts the birthday on February 28 by default, and you can switch to March 1. The choice only matters on the day itself. For a birth date of February 29, 2000:

• On February 28, 2025, the age is 25 years, 0 months, 0 days with the February 28 rule, or 24 years, 11 months, 30 days with the March 1 rule.
• On November 1, 2026 both rules agree: 26 years, 8 months and 3 days.
• Real February 29 birthdays by then: 6 (2004, 2008, 2012, 2016, 2020, 2024). The next is February 29, 2028.

Someone born on February 29, 2096 will wait 8 years for a real birthday, until 2104, because 2100 is not a leap year.

Born in a given year: how old are you?

Subtract the birth year from the current year. The answer is the age reached on the birthday that year; before the birthday, subtract 1 more. Someone born in 1990 is 35 before their 2026 birthday and 36 from that day on. The Birth year tab asks whether the birthday has passed and gives one answer, or both if you are not sure.

Age in weeks and months for babies and children

A baby’s age is usually given in weeks for the first months, then in months until about age 2. This is the chronological age: the time since birth. A baby born on June 20, 2026 is 134 days old on November 1, 2026. That is 19 weeks and 1 day, or 4 months and 12 days.

For a baby born early, pediatricians also use the corrected age. The American Academy of Pediatrics method subtracts the weeks born early, which is 40 minus the weeks of pregnancy at birth. A baby born at 32 weeks was 8 weeks early. At 19 weeks and 1 day old, the corrected age is 11 weeks and 1 day, or 2 months and 17 days counted from the original due date of August 15, 2026. The AAP suggests using corrected age for the first 2 years. These figures are for information only, not medical advice.

Common mistakes when working out age

• Dividing days by 365. Leap days add up: 13,015 ÷ 365 is about 35.66, which hides the extra 9 leap days. Count birthdays instead.
• Forgetting the birthday has not happened yet. The current year minus the birth year is only right after the birthday.
• Counting the birth day as day 1. On the day of birth a person is 0 days old; the first full day ends the next day.
• Treating every month as 30 days. This shifts the day count by a day or two near month ends.

Sources

• U.S. Naval Observatory: Leap Years (Gregorian leap-year rule), checked November 2026.
• American Academy of Pediatrics, HealthyChildren.org: Corrected Age for Preemies, checked November 2026.

Age calculation practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How do I calculate my exact age?

Find your last birthday to get the years, count the month marks since then on the same day number, then count the days left. Born March 15, 1991, you are 35 years, 7 months and 17 days old on November 1, 2026.

How old am I if I was born in 1990?

In 2026 you turn 36. You are 35 until your birthday and 36 from your birthday on. In 2027 you turn 37.

How old is someone born on February 29?

They age like everyone else, one year per year. In common years the birthday is counted on February 28 or March 1, depending on the rule used. Someone born on February 29, 2000 turned 26 in 2026 but has had only 6 real February 29 birthdays.

How many days old am I?

Count the days from your birth date to today; the birth date itself is day 0. Born March 15, 1991, you are 13,015 days old on November 1, 2026. The Exact age tab shows the total days, plus weeks, hours, minutes and seconds.

What day of the week was I born?

The Exact age tab shows it under "Born on a". March 15, 1991 was a Friday, and that birthday falls on a Monday in 2027. The Next birthday tab lists the weekday of your birthday for the next 8 years.

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