Age Calculator
Use this age calculator to find your exact age in years, months, and days from your date of birth, or check your age on any past or future date with leap years included.
Age Calculator
Defaults to today. Change it to find an age on any other date.
Enter values above to see results
Accuracy note: This tool calculates calendar age from the dates entered. For official, legal, medical, or administrative use, verify the result with the relevant authority or your records.
About This Tool
This age calculator measures the time between a date of birth and a selected reference date. By default, the reference date is today, but you can choose another date to see how old someone was or will be at a particular time.
The result includes completed years, remaining months and days, total months, total weeks, total days, the day of the week you were born on, and the time remaining until the next birthday. Leap years and different month lengths are handled automatically.
How to Use the Age Calculator
- Enter the date of birth.
- Leave the reference date set to today, or select another date.
- Click Calculate.
- Review the result in years, months, and days.
- Check the total weeks, days, and next-birthday details.
- Reset the tool to begin another calculation.
An online age calculator is especially useful when a simple subtraction of the birth year from the current year would give the wrong answer.
How Is Age Calculated?
To calculate age in completed years, subtract the birth year from the reference year. Then subtract one year if the birthday has not yet occurred by the selected date.
Completed Age = Reference Year − Birth Year
The calculator then counts the remaining calendar months and days from the most recent birthday.
For example:
- Date of birth: 20 September 2000
- Reference date: 29 July 2026
- Initial year difference: 26
- The birthday has not yet occurred in 2026
- Completed age: 25 years
Age Calculation Example
Suppose the date of birth is 15 May 1990 and the selected reference date is 29 July 2026.
- Completed years: 36
- Additional months: 2
- Additional days: 14
Final result: 36 years, 2 months, and 14 days.
This calendar result is more useful than dividing the total number of days by 365, because calendar years and months do not all have the same length.
Age in Years, Months, and Days
Calendar age is measured across actual calendar boundaries. It accounts for:
- Months with 30 days
- Months with 31 days
- February with 28 or 29 days
- Leap years
- Birthdays that have or have not yet occurred
This is why two people born the same number of total days apart may not always show a simple difference in full months.
How Leap Years Affect Age
A leap year normally contains 366 days instead of 365. Under the Gregorian calendar:
- A year divisible by 4 is generally a leap year.
- A century year is not a leap year unless it is divisible by 400.
- The year 2000 was a leap year.
- The year 2100 will not be a leap year.
For someone born on 29 February, the displayed calendar result depends on how the tool handles the anniversary in a non-leap year. This calculator rolls the anniversary forward to 1 March, so a person born on 29 February 2004 turns 22 on 1 March 2026. For legal or official purposes, check the rule used by the relevant authority.
Age on a Past or Future Date
You can calculate age for a date other than today by changing the reference date. This can help determine:
- Age at graduation
- Age on an application deadline
- Age during a historical event
- Future age on a birthday
- Age when starting a course or job
- Age on an anniversary
The selected reference date must be the same as or later than the date of birth.
Calendar Age vs Total Time Lived
| Calendar Age | Total Time Lived |
|---|---|
| Expressed in years, months, and days | Expressed in one unit |
| Uses actual calendar boundaries | Counts the full elapsed interval |
| Useful for birthdays and records | Useful for total days or weeks |
| Month lengths vary | Every day is counted equally |
Hours, minutes, and seconds should be treated as approximate unless the exact birth time and time zone are also entered.
Common Age-Calculation Mistakes
Avoid these common errors:
- Subtracting the birth year without checking whether the birthday has passed
- Treating every month as 30 days
- Ignoring leap years
- Reversing the birth date and reference date
- Converting total days into calendar years using 365 only
- Assuming displayed seconds are exact without entering a birth time
Start Calculating
Enter the birth date and reference date above, then use the age calculator to review the result in years, months, days, and other available time units.
Frequently Asked Questions
How old am I today?
Enter your date of birth and keep the reference date set to today. The tool will show your completed age and any remaining months and days.
What is my age on a future date?
Choose the future date as the reference date. The tool will compare it with your birth date and return your age on that day.
How can I check how old I am on a past date?
Enter the past date as the reference date, provided it is not earlier than the date of birth.
Can I find my age in total days?
Yes. The result shows total days, weeks, and months in addition to calendar years, months, and days.
Why do two tools sometimes show different month-and-day results?
Calculators may use different conventions when borrowing days across months of unequal length, especially near the end of February or other month boundaries.
Can this result be used for official documents?
The result can help with general checks, but official age requirements should be confirmed using accepted records and the rules of the relevant authority.