Quick answer: To calculate your age, subtract your birth year from the current year, then subtract 1 if your birthday hasn’t happened yet this year. For an exact age in years, months and days, subtract the birth date from today’s date part by part, borrowing days from the previous month when a number goes negative.
Example: born 14 March 2016, date 10 October 2026. That’s 10 years, 6 months and 26 days.
If you’d rather skip the math, use our free age calculator. If you want to understand how the answer is built (and why leap years can cause confusion), keep reading.
Key takeaways
- Age in whole years = current year − birth year, minus 1 if the birthday hasn’t happened yet.
- For exact age, you need month lengths: 31 days for seven months, 30 for four, and 28 or 29 for February.
- A leap year has 366 days. It must be divisible by 4, except century years not divisible by 400.
- People born on Feb 29 are called leaplings. Their legal birthday in non-leap years differs by country.
- A calculator is faster, but doing it by hand shows you why the answer is what it is.
Why Calculate Your Age by Hand?
Most of us never need to. But there are good reasons to learn the method:
- You want to check a result from an online tool.
- You have a form that asks for age on a specific date, such as a school cut-off or an event.
- You’re curious about how many days old you are.
- You’re teaching a child how dates and calendars work.
An age calculator is really a specialised date time calculator. It subtracts one date from another and handles month lengths and leap years for you. Understanding the method helps you trust the result.
Method 1: Age in Whole Years
This is the quick version most forms ask for.
- Subtract your birth year from the current year.
- Check whether your birthday has already happened this year.
- If it hasn’t, subtract 1.
Example 1: born 14 March 2000, today 10 October 2026
- 2026 − 2000 = 26
- Birthday (14 March) has passed → 26 years old
Example 2: born 25 December 1995, today 10 October 2026
- 2026 − 1995 = 31
- Birthday (25 December) hasn’t happened yet → 31 − 1 = 30 years old
If you want your exact age, use the next method.
Month Lengths You Need to Know
Exact age depends on how many days are in each month.
| Days | Months |
|---|---|
| 31 days | January, March, May, July, August, October, December |
| 30 days | April, June, September, November |
| 28 or 29 days | February (29 in a leap year) |
Memory tricks:
- The rhyme: “Thirty days hath September, April, June and November.”
- The knuckle method: make a fist. Each knuckle is a 31-day month, and each dip between knuckles is a shorter month.
Method 2: Exact Age in Years, Months and Days
This is the “calculate your age” method that gives the full answer.
Step by step
- Write both dates as year, month, day.
- Subtract days. If the result is negative, borrow the number of days in the month before the later date’s month, and subtract 1 from the months.
- Subtract months. If the result is negative, add 12 months and subtract 1 from the years.
- Subtract years.
Worked example 1: no borrowing needed for months
Born: 14 March 2016
Date: 10 October 2026
| Year | Month | Day | |
|---|---|---|---|
| Date | 2026 | 10 | 10 |
| Born | 2016 | 3 | 14 |
- Days: 10 − 14 = −4. That’s negative, so borrow from September (30 days): −4 + 30 = 26, and the month drops from 10 to 9.
- Months: 9 − 3 = 6
- Years: 2026 − 2016 = 10
Answer: 10 years, 6 months, 26 days.
Worked example 2: borrowing for both days and months
Born: 25 November 1990
Date: 8 February 2026
- Days: 8 − 25 = −17. Borrow from January (31 days): −17 + 31 = 14, and the month drops from 2 to 1.
- Months: 1 − 11 = −10. Add 12: 2, and the year drops by 1.
- Years: (2026 − 1) − 1990 = 35
Answer: 35 years, 2 months, 14 days.
A quick check: 25 November 1990 plus 35 years is 25 November 2025. Add 2 months to reach 25 January 2026. Add 14 more days to reach 8 February 2026. ✔
Edge case: people born on the 29th, 30th or 31st can get a result that differs by a day or two between tools, because “the same day next month” doesn’t always exist. When it matters, note which method you used.
How Do Leap Years Work?
A leap year has 366 days, with an extra day, 29 February.
The Earth takes about 365.24 days to orbit the sun, so adding a leap day keeps the calendar in step with the seasons.
The rule:
- A year divisible by 4 is a leap year.
- But a year divisible by 100 is not, unless...
- ...it’s also divisible by 400, in which case it is.
| Year | Divisible by 4? | By 100? | By 400? | Leap year? |
|---|---|---|---|---|
| 2024 | Yes | No | n/a | Yes |
| 2026 | No | n/a | n/a | No |
| 2028 | Yes | No | n/a | Yes |
| 1900 | Yes | Yes | No | No |
| 2000 | Yes | Yes | Yes | Yes |
| 2100 | Yes | Yes | No | No |
The most recent leap day was 29 February 2024, and the next is 29 February 2028. timeanddate
Why it matters for age: leap days change how many days are between two dates, which shows up when you convert age into days. They don’t change your age in years.
How to Calculate Your Age in Days, Weeks and Months
Many people want a “how many days old am I” answer, or a “time calculator” style conversion. Use the exact age first, then convert.
Months: years × 12 + months. For 10 years 6 months: 10 × 12 + 6 = 126 months.
Days (including leap days):
- Multiply whole years by 365.
- Add one day for each 29 February that falls between the two dates.
- Add the remaining days.
Example: born 14 March 2016, date 10 October 2026.
- Whole years to 14 March 2026: 10 × 365 = 3,650
- Leap days in between (29 Feb 2020 and 29 Feb 2024): +2 → 3,652 days
- From 14 March to 10 October 2026: 210 days
- Total: 3,862 days
Weeks: 3,862 ÷ 7 = 551 weeks and 5 days.
Hours: a 365-day year has 8,760 hours (365 × 24), and a leap year has 8,784 (366 × 24).
This is the kind of long calculation where a date and time calculator saves effort.
How to Calculate Age If You Were Born on Feb 29
A person born on 29 February is called a leapling or leaper. The odds of being born on 29 February are about 1 in 1,461. The calculation has one extra wrinkle: in years that have no 29 February, which day counts as the birthday?
Your age in years is unaffected
Your age goes up by one every year, whether or not your birth date appears on the calendar. Someone born on 29 February 2004 is 22 on 10 October 2026, because they’ve already passed their birthday this year under any convention.
Exact age on 10 October 2026: 29 February 2004 → 22 years, 7 months, 11 days (using the borrowing method in this guide).
Other conventions give slightly different day counts. Counting from 1 March gives 22 years, 7 months, 9 days. Counting from 28 February gives 22 years, 7 months, 12 days. All are “right” under their own rule, which is why it helps to state your method.
Which date is the legal birthday in a non-leap year?
It depends on where you live.
- United Kingdom: A leaper reaches the age of majority on 1 March in a non-leap year.
- New Zealand: The law recognises 28 February as the transition date for a driving licence.
- United States: 1 March is widely accepted in common years, but practice varies.
Check the rules for your own country or document, especially for voting, driving, drinking age or retirement.
Counting “real” birthdays
A leapling’s actual 29 February birthdays are rare. Someone born on 29 February 2004 had their 1st leap-day birthday in 2008, and their 5th in 2024, when they were 20. Their 6th will be on 29 February 2028.
How to Calculate Age on a Specific Date
Use the same method, but replace “today” with the target date.
Example: how old will someone born on 14 March 2016 be on 1 September 2030?
- Days: 1 − 14 = −13 → borrow from August (31): 18, month becomes 8
- Months: 8 − 3 = 5
- Years: 2030 − 2016 = 14
Answer: 14 years, 5 months, 18 days.
This is useful for school entry dates, event limits and eligibility rules.
Age and BMI: Why Exact Age Matters
For children and teens, health charts use age in years and months. A few months can change a BMI percentile, so exact age is the first step. We explain this in BMI by Age and Sex.
Common Mistakes When You Calculate Your Age
- Subtracting only the years. This is wrong whenever your birthday hasn’t happened yet.
- Using 30 days for every month. It causes errors of one to three days.
- Borrowing from the wrong month. Borrow from the month before the later date’s month.
- Forgetting century leap-year rules. 1900 and 2100 are not leap years. 2000 was.
- Ignoring time zones. A person born near midnight may have a different calendar date in another country.
- Mixing age systems. Some cultures count age differently. See our upcoming guide on Korean age vs international age.
By Hand vs a Calculator
Doing it by hand teaches you the logic. A calculator is faster, avoids borrowing errors and handles edge cases. Use our age calculator to get the answer in seconds, or cross-check your hand calculation. For other measurements, browse the date and unit tools.
How to Calculate Your Age: FAQs
How do I calculate my age from my date of birth?
Subtract your birth year from the current year, then subtract 1 if your birthday hasn’t happened yet. For exact age, subtract the dates part by part and borrow days from the previous month when needed.
How do I calculate my exact age in years, months and days?
Subtract days, then months, then years. If days go negative, borrow the length of the previous month. If months go negative, borrow 12 months from the years.
How many days are in a leap year?
366 days.
How do I know if a year is a leap year?
It’s divisible by 4, except century years, which must also be divisible by 400. So 2000 was a leap year, but 1900 and 2100 are not.
How old am I if I was born on Feb 29?
Your age in years increases every year, as normal. For example, born 29 February 2004, you are 22 on 10 October 2026.
When do leaplings celebrate their birthdays?
Most celebrate on 28 February or 1 March in common years. The legal date depends on your country.
How do I calculate my age in days?
Multiply your whole years by 365, add one day for each 29 February in between, then add the remaining days.
What is the difference between a time calculator and an age calculator?
An age calculator finds the gap between your date of birth and a date. A time calculator usually adds or subtracts hours and minutes. Both are kinds of date and time calculators.
Calculate Your Age in Seconds
You now know how to calculate your age by hand. For a fast, exact answer, use our free age calculator. Need other conversions? Explore our unit conversion tools, or visit the ConversionFree for more free calculators.
