Age Calculator
Find out your exact age in years, months, and days. See your age broken down into total months, weeks, and days, plus a countdown to your next birthday.
Accounts for leap years and varying month lengths
Calculate Your Age
Select your birth date
Defaults to today
How to Use This Age Calculator
Enter Your Birth Date
Select or type your date of birth using the date picker. This is the starting point for all age calculations.
Set the Reference Date
By default it uses today, but you can change it to any date to find your age at a specific time in the past or future.
View Your Results
See your exact age in years, months, and days, plus totals in months, weeks, days, and hours, along with a countdown to your next birthday.
How Age Calculation Works
Age = Reference Date - Date of BirthCalculating an exact age is more nuanced than simply subtracting years. The algorithm accounts for the variable length of months and leap years to give a precise result.
1. Years = Reference Year - Birth Year (adjusted for month/day)2. Months = remaining months after complete years3. Days = remaining days after complete months4. Total Days = (Reference Date - Birth Date) in milliseconds / 86,400,0005. Total Weeks = Total Days / 76. Total Months = (Years x 12) + MonthsKey details about the calculation:
- Month boundaries: if the current day-of-month is less than the birth day, we borrow days from the previous month
- Leap years: February 29 birthdays naturally resolve since the algorithm uses actual calendar dates
- Total days: computed from the millisecond difference between dates, ensuring absolute precision
- Next birthday: found by checking whether this year's birthday has passed, then selecting the next occurrence
Common Age Milestones
| Age | Approx. Days | Approx. Weeks | Milestone |
|---|---|---|---|
| 1 year | 365 | 52 | First birthday |
| 10 years | 3,653 | 522 | First decade |
| 13 years | 4,749 | 678 | Teenager |
| 18 years | 6,575 | 939 | Legal adult (US) |
| 21 years | 7,671 | 1,096 | Drinking age (US) |
| 30 years | 10,958 | 1,565 | Thirty milestone |
| 50 years | 18,263 | 2,609 | Half century |
| 65 years | 23,742 | 3,392 | Retirement age (US) |
| 100 years | 36,525 | 5,218 | Centenarian |
Approximate values based on 365.25 days per year (accounting for leap years)
Frequently Asked Questions
How does the age calculator work?
The calculator finds the difference between your date of birth and a reference date (today by default). It computes the exact number of complete years, remaining months, and remaining days. It also calculates total months, total weeks, and total days lived, plus a countdown to your next birthday.
Does the age calculator account for leap years?
Yes. The calculator uses actual calendar dates, so leap years (with 366 days) and months of varying length (28, 29, 30, or 31 days) are all handled correctly. The total days calculation is based on the exact millisecond difference between the two dates.
Can I calculate my age as of a past or future date?
Yes. By default the calculator uses today as the reference date, but you can change the "Calculate age as of" field to any date after your birth date. This is useful for finding your age at a specific event or milestone.
How is the "next birthday" countdown calculated?
The calculator looks at your birth month and day and finds the next occurrence of that date after the reference date. If your birthday has already passed this year, it counts down to next year. The result shows the exact number of days remaining.
Why might my age in days differ from years times 365?
A calendar year is not always 365 days. Leap years add an extra day, and different months have different lengths. The "total days" figure is the precise count of days between your birth date and the reference date, which will differ slightly from a simple multiplication.
About This Calculator
This age calculator is provided for informational and entertainment purposes. All calculations are performed client-side in your browser. No personal data is collected or stored. The calculator uses the Gregorian calendar and accounts for leap years and varying month lengths. For legal age verification, consult official documentation in your jurisdiction.