How to Calculate Age in Years, Months and Days
5 min read · Updated September 26, 2026 · by the SolveCalcPro editorial team
Subtracting birth year from this year gives a rough age, but not an exact one — it ignores whether the birthday has happened yet this year. To get years, months and days right, you need to handle month lengths and “borrowing”, the same idea you use in written subtraction. This guide shows the step-by-step method and the traps.
The method
- Write the later date (usually today) and the birth date as year–month–day.
- Subtract days. If the result is negative, borrow the number of days in the month before the later date and reduce the months by one.
- Subtract months. If negative, borrow 12 months and reduce the years by one.
- Subtract years.
Worked example
Birth date 15 August 1990; today 3 March 2026.
- Days: 3 − 15 = −12, so borrow the days in February 2026 (28): −12 + 28 = 16 days, and reduce the months by one.
- Months: 3 − 8 − 1 = −6, so borrow 12: −6 + 12 = 6 months, and reduce years by one.
- Years: 2026 − 1990 − 1 = 35 years.
Answer: 35 years, 6 months, 16 days. You can confirm by adding 35 years, 6 months and 16 days back onto the birth date.
Leap years and 29 February
A year is a leap year if it is divisible by 4, except century years not divisible by 400 (so 2000 was a leap year, 1900 was not). People born on 29 February are usually treated as having their birthday on 28 February or 1 March in non-leap years; the calculator uses the actual calendar to avoid errors.
Other useful numbers
- Total days lived: the number of days between the two dates, counted from the calendar, not from 365 × years.
- Next birthday: the next occurrence of the birth month and day; the days until it are the difference from today.
- Day of the week born: use the day of the week calculator.
Practice questions
Test yourself, then tap to check. Answers are calculated by the tools linked below.
- Born 12 March 2005. What is the age on 1 January 2026?
Show answer
Age: 20 years, 9 months, 20 days
- How many days are between 25 November 2026 and 25 December 2026?
Show answer
Total days: 30
- What date is 6 months after 30 April 2026?
Show answer
Result: Friday, October 30, 2026
Frequently asked questions
How do I calculate exact age from a date of birth?
Subtract the birth date from the later date year, month and day, borrowing days from the previous month and 12 months from a year where needed.
How many days old am I?
Count the days between your birth date and today. The age calculator shows the total instantly and handles leap years.
Why does counting just the year difference give the wrong age?
Because it assumes the birthday has already passed this year. If it hasn’t, you are one year younger than the simple subtraction suggests.
What age counts for someone born on 29 February?
Practices vary — many legal systems treat the birthday as 1 March in non-leap years, others as 28 February. Check the rule that applies to you.
Try it yourself
Age CalculatorWork out exact age in years, months and days, plus the days until your next birthday.
Days Between Dates CalculatorFind the exact number of days, weeks and business days between any two dates.Date Calculator (Add or Subtract Days)Add or subtract days, weeks, months and years from any date.Birthday Countdown CalculatorSee exactly how many days until the next birthday, and what age it turns.Keep learning
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