How age is calculated
Age is counted in completed units: first full years, then full months, then the remaining days. You turn one year older on the anniversary of your birth date, not after 365 days, because leap years make some years 366 days long.
- Subtract the birth year from the current year.
- If this year's birthday has not happened yet, subtract one year.
- Count the full months since the last birthday, then the days since the last "month anniversary".
When the day of the month runs past the end of a shorter month (for example, from 31 January to 28 February), the calculator borrows the number of days in the previous month, which is the standard way people count months.
Worked example
Born on 15 May 1990, age on 5 October 2026:
- 2026 − 1990 = 36, and the 2026 birthday (15 May) has passed, so 36 years.
- From 15 May to 15 September is 4 months.
- From 15 September to 5 October is 20 days.
Result: 36 years, 4 months and 20 days, or 13,292 days in total. The next birthday, on Saturday 15 May 2027, is 222 days away. 15 May 1990 itself was a Tuesday.
Why total days can surprise you
Every four years (with some exceptions for century years) a leap day is added, so the number of days you have lived is not simply years × 365. Someone aged exactly 36 has lived about 13,149 days, including nine leap days. Total days are useful for milestones such as a "10,000-day birthday", which falls at about 27 years and 4 months.
Born on 29 February?
People born on a leap day have a birth date that only exists every four years. Legally, many countries treat 1 March as the birthday in non-leap years for things like reaching adulthood, while others use 28 February. Socially, most people celebrate on one of the two. This calculator counts a 29 February birthday as reached on 1 March in non-leap years.
Different ways age is counted
- International age (used here): starts at 0 at birth and increases on each birthday.
- East Asian age reckoning: traditionally a baby is 1 at birth and everyone gains a year at the New Year. South Korea officially adopted international age for legal and administrative purposes in 2023.
- Hijri age: Islamic religious obligations use the lunar Hijri calendar, whose years are about 11 days shorter, so a person's Hijri age is slightly higher. See the Hijri date converter.
Common uses
- Filling in forms that ask for age in years and months, such as school admissions or child health checks.
- Checking eligibility ages for licences, pensions or sports categories on a specific date, not just today.
- Planning milestone celebrations.
Common mistakes
- Dividing days by 365. This drifts by about a day every four years.
- Forgetting that the birthday may not have happened yet this year.
- Using a reference date in the wrong time zone. The calculator works with calendar dates only, so time zones do not shift the result.
Your age in other units
For the example age of 36 years, 4 months and 20 days (13,292 days):
| Unit | Value |
|---|---|
| Months | 436 months and 20 days |
| Weeks | 1,898 weeks and 6 days |
| Days | 13,292 |
| Hours | about 319,008 |
| Minutes | about 19.1 million |
Age difference between two people
Enter the older person's date of birth as the date of birth and the younger person's date of birth as "age on this date": the result is the exact age gap in years, months and days.
Age on a specific date
Many rules depend on age on a fixed date rather than today: school entry, sports age groups, travel fares and pension eligibility. Enter that date in the second field to check.
Frequently asked questions
How do I calculate my exact age?
Count completed years since your birth date, then completed months since your last birthday, then the remaining days. Born 15 May 1990, on 5 October 2026 you are 36 years, 4 months and 20 days old.
How many days old am I?
Subtract your date of birth from today's date in days. The calculator does this exactly, including leap days.
When is my 10,000th day?
About 27 years and 4 months after birth. Add 10,000 days to your date of birth with the add-days calculator for the exact date.
How is age counted for people born on 29 February?
In non-leap years many countries treat 1 March as the birthday for legal purposes; this calculator does the same.
How do I calculate the age difference between two people?
Use the older birth date as the date of birth and the younger birth date as the reference date.
How many hours old am I?
Multiply the total days by 24. 13,292 days is about 319,008 hours.
Sources
- ISO 8601 date and time format (calendar dates and the Gregorian calendar rules for leap years).
- Republic of Korea, Ministry of Government Legislation: adoption of the international age system (June 2023).
Last reviewed 5 October 2026. Results are estimates; see our disclaimer.