Quick answer
Your age is the calendar difference between your date of birth and a chosen date, written as whole years, then months, then days. Enter your date of birth (and, optionally, any other date) to see your age, the total days, weeks and hours you have lived, your next birthday and the weekday you were born.
Counting age by hand is easy until months have different lengths. This calculator does the calendar arithmetic for you using the same rules every time, and it also shows the exact number of days, which is the figure that never depends on how months are counted.
Leave the second date empty to use today, or enter a past or future date to answer questions such as how old someone was on a given day or how old they will be on a future date.
Related tools: Date Calculator: Add or subtract days, weeks, months or years from a date. Days Between Dates Calculator: Number of days, weeks and months between two dates. Time Duration Calculator: Elapsed time between two clock times, including across midnight.
How to use the Age Calculator
- Pick date of birth.
- Optionally, pick age at date.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Date of birth | A calendar date | — |
| Age at date (optional) | A calendar date. Leave blank to use today's date | — |
Formula and method
Formula
age = calendar difference between birth date and the chosen date (years, then months, then days)
Exact integer day arithmetic in UTC; no daylight-saving or time-zone effects.
Whole years and months are counted on the calendar; remaining days borrow the length of the month before the end date. Total days are exact.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Date of birth = 1990-06-15; Age at date = 2024-03-10.
| Result | Value |
|---|---|
| Your age | 33 years, 8 months, 24 days |
| Total days | 12,322 |
| Total weeks | 1,760 |
| Total hours | 295,728 |
| Next birthday | 2024-06-15 (97 days) |
| Born on a | Friday |
Example 2
Inputs: Date of birth = 2000-01-01; Age at date = 2000-01-01.
| Result | Value |
|---|---|
| Your age | 0 days |
| Total days | 0 |
| Total weeks | 0 |
| Total hours | 0 |
| Next birthday | 2001-01-01 (366 days) |
| Born on a | Saturday |
Example 3
Inputs: Date of birth = 2000-02-29; Age at date = 2024-02-29.
| Result | Value |
|---|---|
| Your age | 24 years |
| Total days | 8,766 |
| Total weeks | 1,252 |
| Total hours | 210,384 |
| Next birthday | 2025-02-28 (365 days) |
| Born on a | Tuesday |
The first line is the headline result (your age). Below it the age Calculator lists total days, total weeks, total hours, next birthday and born on a, which describe the same case from other angles. Exact integer day arithmetic in UTC; no daylight-saving or time-zone effects.
How age in years, months and days is counted
The calculator first counts whole years from the date of birth, then whole months, and finally the leftover days. When the day of the month on the later date is smaller than the birth day, it borrows the length of the month before the later date.
Worked by hand for a birth date of 15 June 1990 and a chosen date of 10 March 2024: the last whole birthday was 15 June 2023, which makes 33 years. From 15 June 2023 to 15 February 2024 is 8 whole months. From 15 February to 10 March 2024 is 14 days to the end of February (2024 has 29 days) plus 10 days into March, which is 24 days. The age is therefore 33 years, 8 months, 24 days, exactly what the calculator shows.
Why the total number of days is the reliable figure
Years and months are calendar units of different lengths, so two people with the same age in years and months can have slightly different numbers of days. Days are exact: 15 June 1990 to 10 March 2024 is 12,322 days, which is 1,760 whole weeks and 295,728 hours.
The next-birthday figure uses the same exact count: from 10 March 2024 to 15 June 2024 is 97 days.
Leap-day birthdays
Someone born on 29 February has no 29 February in most years. This calculator moves their age forward on 1 March in years that are not leap years. Legal rules for ages differ between countries, so use the figure here as a calendar calculation, not as legal proof of age.
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Date of birth: entering "2030-01-01" shows "Date of birth must not be after the chosen date." beside that field and no result.
Choosing between the Age Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Date Calculator](/date-calendar/date-calculator/) | start date and operation | Resulting date |
| [Days Between Dates Calculator](/date-calendar/days-between-dates-calculator/) | start date, end date and count end date? | Days between |
| [Time Duration Calculator](/time/time-duration-calculator/) | start time and end time | Duration |
| [Hours Calculator](/time/hours-calculator/) | start time and end time | Hours worked |
| [Baby Age Calculator](/lifestyle/baby-age/) | date of birth and reference date | Age |
Background: dates and times
Date and time results depend on the conventions a tool uses: whether the end date counts, whether weekends and holidays are skipped, how months of different lengths are handled and whether time zones are applied. This page states its convention, and the worked examples show it.
Dates use the Gregorian calendar and calendar days unless the page says otherwise; check deadlines against the rule in your contract or regulation.
Assumptions and limitations
- Birth date after the chosen date is rejected
- Leap-day birthdays: age increments on 1 March in non-leap years in the calendar difference
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for date of birth to confirm this.
Frequently asked questions
How do I calculate my age from my date of birth?
Enter your date of birth. The calculator subtracts it from today's date (or from the date you enter) and returns whole years, months and days, plus the exact total days.
Can I find my age on a past or future date?
Yes. Enter the date in the optional 'Age at date' field. The result is your age on that day, as long as it is not before your date of birth.
What does the Age Calculator calculate?
Calculate your exact age in years, months and days. It returns Your age, Total days, Total weeks, Total hours and Next birthday.
What formula does the Age Calculator use?
age = calendar difference between birth date and the chosen date (years, then months, then days). Whole years and months are counted on the calendar; remaining days borrow the length of the month before the end date.
What do I need to enter in the age Calculator?
You enter Date of birth. Optional: Age at date.
How is the result rounded or limited?
Exact integer day arithmetic in UTC; no daylight-saving or time-zone effects. Birth date after the chosen date is rejected.
What are the limits of this calculator?
Birth date after the chosen date is rejected. Leap-day birthdays: age increments on 1 March in non-leap years in the calendar difference.
What is an example of a age result?
With date of birth 1990-06-15 and age at date 2024-03-10, the your age is 33 years, 8 months, 24 days.
Related calculators
- Date Calculator — Add or subtract days, weeks, months or years from a date.
- Days Between Dates Calculator — Number of days, weeks and months between two dates.
- Time Duration Calculator — Elapsed time between two clock times, including across midnight.
- Hours Calculator — Hours worked between a start and end time, minus breaks.
- Baby Age Calculator — A baby's age in weeks, months and days.
- Age Difference Calculator — Time between two birth dates.
- School Age Calculator — Child's age on a school cutoff date.
- Birth Year Calculator — Year of birth from a person's age.
- Unix Timestamp Converter — Convert between Unix timestamps (seconds) and UTC dates.
Sources
- ISO 8601-1: Date and time, representations for information interchange (calendar dates, ordinal dates and week dates)
- Gregorian calendar reform, papal bull Inter gravissimas (1582): the leap-year rule used for all dates
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.