How to Calculate Your Age in Years, Months and Days
Your age is more than the number of birthdays you have celebrated. An exact age calculation compares your date of birth with a specific calculation date and accounts for different month lengths and leap years.
Quick answer: subtract the birth date from the date you are calculating from, borrowing from the previous month when the day or month needs adjustment.
What an age calculation measures
An age result can be shown in years, months and days, total months, total weeks or total days. The format you need depends on the question. A birthday announcement usually uses completed years, while an application or a record may require a more precise date difference.
How to calculate age manually
- Write down the birth date and the date you want to calculate from.
- Subtract the birth year from the calculation year.
- Compare the months. If the birthday month has not arrived yet, reduce the completed-year count by one.
- Compare the days. If needed, borrow days from the previous month and then calculate the remaining days.
Manual date subtraction is easy to get wrong because months do not all contain the same number of days. That is why a date-aware calculator is useful for exact results.
Worked example
Suppose the birth date is 15 March 2000 and the calculation date is 24 September 2026. On that date, the completed age is 26 years, 6 months and 9 days.
If you use a different calculation date, the answer will change. Always check that the calculator is using the date you intend.
Years, months and days versus total days
An age expressed as years, months and days is a calendar result. A total-days result counts the exact number of days between two dates. Leap years matter, so multiplying the number of years by 365 is only an approximation.
Use the Age Calculator for a calendar-style result. If you need the total number of days, use the Age in Days Calculator.
Does the calculation include the start date?
Date tools can use slightly different counting conventions. Some count the difference between dates, while others include the start or end date for a specific purpose. Read the result label and use the same convention consistently when comparing dates.
Why exact age can matter
Exact date differences can be useful for planning birthdays, tracking milestones, checking elapsed time and completing forms that ask for a precise age. For official applications, follow the organisation’s instructions if they define how dates must be counted.
Check your result
Before relying on an answer, confirm the day, month and year in both date fields. A one-day input error can change the result, especially around the end of a month or a leap day.
For a quick, repeatable answer, enter both dates into the Age Calculator and choose the output format that matches your purpose.