How to Calculate Age in Years, Months, and Days
Learn how to calculate exact age from a date of birth, handle leap years, and find the difference between two dates by hand.
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Table of contents
The basic method
To find exact age, subtract the birth date from the target date in three parts: years, months, and days.
- Subtract the birth year from the current year.
- If the birthday has not happened yet this year, subtract one year and add the missing months.
- If the day of the month is smaller than the birth day, borrow days from the previous month.
Worked example
Someone born on March 15, 2000 is exactly 26 years and 7 months old on October 15, 2026, with 0 extra days. Counting from March 15, 2000 to March 15, 2026 gives 26 years, and March 15 to October 15 adds 7 months.
Leap years and February 29
A year has 366 days in a leap year, which affects age in total days. People born on February 29 are usually treated as having a birthday on February 28 or March 1 in non-leap years, depending on local rules.
When an age calculator helps
Manual counting is easy for round dates but error-prone when months have different lengths. An age calculator removes that risk and can also show total months, weeks, or days.
FAQ
How do I calculate age from date of birth?
Subtract the birth date from today's date in years, months, and days, borrowing from the previous month when needed.
Can I calculate the days between two dates?
Yes. The same method works for any two dates, and a calculator can return the exact number of days.
How are leap year birthdays counted?
Rules vary by region. Many places treat the birthday as February 28 or March 1 in non-leap years.
