Learn how to calculate exact age between two dates, including completed years, months and days and additional time intervals.
How age is normally counted
The common age system increases age on the birthday. The calculator therefore reports completed years first and then the remaining months and days.
Enter the two dates
Use the date of birth and the date at which you want to know the age. The second date can be today or a future/past reference date.
Why months and days are not simple divisions
Calendar months have different lengths, so exact age needs calendar arithmetic rather than dividing total days by 30.
Additional intervals
The calculator also shows total days so you can use the result for planning, records and date comparisons.
International considerations
Different cultures use different age-counting conventions. Tervilo uses the common birthday-based system and explains that distinction.
Examples
For a person born on January 1, 2000, the age on January 1, 2026 is exactly 26 years. A date between birthdays includes the remaining months and days.
How to verify an age result
Check the birth date, reference date and date format first. Then verify the completed years by asking whether the birthday has occurred in the reference year. Finally, check the remaining months and days against the calendar.
Why this page is a supporting guide
For broad search questions about calculating age, the more comprehensive How to Calculate Age from Date of Birth guide provides the primary explanation. This page focuses on interpreting an age-calculator result.
Check the Reference Date
An age result is always relative to a reference date. Today is only one possible reference date; a past or future date can be used when the calculation requires it.
Completed Years vs Years, Months and Days
Completed years increase on the birthday under the common birthday-based convention. The remaining months and days describe the calendar interval after the last completed birthday.
Why Total Days and Calendar Age Differ
A total-day result is an elapsed-time measure. Calendar age uses calendar boundaries, so it should not be converted between years, months and days by dividing total days by a fixed number such as 365.
Leap Years and February 29
Leap-day birthdays require a convention when the reference year is not a leap year. If the result is being used for legal eligibility, identity records or an institutional decision, follow the applicable official convention.
How to Verify an Age Result
- Check the birth date.
- Check the reference date.
- Confirm the date format.
- Verify whether the birthday has occurred in the reference year.
- Check the remaining calendar months and days.
Use the Tervilo Age Calculator
Use the Tervilo Age Calculator to calculate calendar age between two dates and review the resulting intervals.
Check the Reference Date
An age result is always relative to a reference date. Today is only one possible reference date; a past or future date can be used when the calculation requires it.
Completed Years vs Years, Months and Days
Completed years increase on the birthday under the common birthday-based convention. The remaining months and days describe the calendar interval after the last completed birthday.
Why Total Days and Calendar Age Differ
A total-day result is an elapsed-time measure. Calendar age uses calendar boundaries, so it should not be converted between years, months and days by dividing total days by a fixed number such as 365.
Leap Years and February 29
Leap-day birthdays require a convention when the reference year is not a leap year. If the result is being used for legal eligibility, identity records or an institutional decision, follow the applicable official convention.
How to Verify an Age Result
- Check the birth date.
- Check the reference date.
- Confirm the date format.
- Verify whether the birthday has occurred in the reference year.
- Check the remaining calendar months and days.
Use the Tervilo Age Calculator
Use the Tervilo Age Calculator to calculate calendar age between two dates and review the resulting intervals.