Age Calculator
Calculate exact age in years, months and days from a date of birth, plus days and weeks lived and the countdown to the next birthday.
Updated Formula covered by automated tests
Type a date of birth and the calculator gives the exact age today in years, months and days, the number of days and weeks lived, and how many days remain until the next birthday along with the age you will turn. Everything runs on your device using your local calendar date.
Exact age matters more often than people expect: school enrollment cut-offs, youth sports age groups, eligibility for a driver’s permit, the six-month adjustment some pediatric charts use, or simply settling a family argument about who is older by how many days. Milestone counts such as a 10,000th day are popular too, and they are easy to get wrong by hand because of leap years.
The formula
- Yb, Mb
- Birth year and birth month
- Y, M
- Current year and month
- a
- Completed months of life
- N(date)
- Serial day number of a date, so subtracting two of them gives the exact count of days including leap days
This is the "completed units" convention used on official forms: you are 22 until the day of your 23rd birthday, and the months and days after that are counted from your most recent monthly anniversary of birth. When that anniversary falls on a day the month lacks (the 31st in a 30-day month, or February 29 in a common year), the last day of that month is used instead.
People born on February 29 therefore have their birthday counted on February 28 in common years. That is a convention, not a law of nature: some legal systems treat March 1 as the day a leap-day baby reaches a new age, so for anything official check the rule that applies where you live.
Worked example
Leo was born on February 29, 2004. On October 18, 2026 he wants his exact age and a countdown to his next birthday, which in 2027 has no February 29.
- 1 Completed months: 12 × (2026 − 2004) + (10 − 2) = 272. Moving 272 months from his birth date gives October 29, 2026, which has not arrived, so a = 271.
- 2 That is 271 ÷ 12 = 22 years with 7 months left over; the 271-month anniversary is September 29, 2026.
- 3 Days since September 29: 1 (Sep 30) + 18 (Oct 1 to 18) = 19 days.
- 4 Days lived: from February 29, 2004 to October 18, 2026 is 8,267 days, exactly 1,181 weeks.
- 5 Next birthday: 2027 is not a leap year, so it is February 28, 2027, which is 13 + 30 + 31 + 31 + 28 = 133 days away.
Result: Leo is 22 years, 7 months and 19 days old (8,267 days). He turns 23 on February 28, 2027, 133 days from now.
Before you rely on the result
- Ages are computed from your device’s local date; someone born in a different time zone may count their birthday as starting a few hours earlier or later.
- The tool is for general information. Legal age thresholds (voting, drinking, retirement benefits) can have their own counting rules, including the leap-day rule described above.
Frequently asked questions
How old is someone in "Korean age" or other counting systems?
Traditional East Asian counting starts at 1 at birth and adds a year every New Year, so it can be one or two years higher than the international count shown here. South Korea standardized official documents on the international method in June 2023.
Why does the result say 0 days until my birthday?
It is your birthday today. The calculator compares calendar dates, not times of day, so the full day counts as the birthday from midnight to midnight in your local time.
Are the hours and minutes lived exact?
No. They multiply the number of days by 24 and 1,440 and ignore the hour you were born, so they can be off by up to a day. Daylight-saving shifts also add or remove an hour twice a year in many places.
How do I find the day I turn 10,000 days old?
Add 10,000 days to your birth date with the add or subtract days calculator on this site. Someone born on January 1, 2000 reaches 10,000 days on May 19, 2027.