How to calculate age
Here it is with your numbers:
- Subtract the birth year from the year on the date: 2026 − 1990 = 36.
- The birthday on June 15 has already happened in 2026, so the age stays 36 years.
- Count the whole months since the last birthday: 4.
- Count the days left over: 25.
It means 13,296 days (1,899 weeks and 3 days) have passed since the day of birth. The next birthday is on Tuesday, June 15, 2027, in 218 days, when the age reaches 37.
Age is counted in completed years: it goes up by one on each birthday, not before. The months and days are what has passed since the last birthday.
Source CDC · National Center for Health Statistics: Age ↗U.S. Census Bureau · 1910 Census Instructions to Enumerators, age at last birthday ↗
Your age in other units
| Unit | Your age |
|---|---|
| Years | 36 |
| Months | 436 |
| Weeks | 1,899 weeks and 3 days |
| Days | 13,296 |
Born on February 29? In years that aren’t leap years, this calculator counts the birthday as March 1, as other age calculators do. For anything official, check the rule used by whoever is asking.
Age examples
| Born | Age on | Answer |
|---|---|---|
| October 6, 2008 | October 1, 2026 | 17 years, 11 months and 25 days |
| February 29, 2000 | March 1, 2001 | 1 year and 1 day |
| June 15, 1990 | June 15, 2040 | 50 years |
Calculate age in Excel or Google Sheets
Put the date of birth in cell A1. Spreadsheets understand TODAY(), so the answer updates every day.
| To find | Formula |
|---|---|
| Whole years | =DATEDIF(A1,TODAY(),"Y") |
| Whole months | =DATEDIF(A1,TODAY(),"M") |
| Days | =DATEDIF(A1,TODAY(),"D") |
Source Microsoft Support · DATEDIF function ↗
FAQs
How old am I?
Type your date of birth into the calculator. It counts the completed years from your date of birth to today, and then the months and days since your last birthday.
How many days old am I?
The calculator subtracts your date of birth from today’s date and shows the number of days in the “Days old” box. Someone born on June 15, 1990 was 13,257 days old on October 1, 2026.
How do you calculate age?
Subtract the birth year from this year, then take 1 off if the birthday hasn’t happened yet. The Census Bureau’s rule: a person 17 years, 11 months and 25 days old is counted as 17, because that is the age at the last birthday.
Source U.S. Census Bureau · 1910 Census Instructions to Enumerators, age at last birthday ↗
How do you calculate age in Excel?
Put the date of birth in cell A1 and use =DATEDIF(A1,TODAY(),"Y") for the whole years. Use "M" for whole months or "D" for days.
Sources
- CDC: National Center for Health Statistics: Age
- U.S. Census Bureau: 1910 Census Instructions to Enumerators, age at last birthday
- Microsoft Support: DATEDIF function