Age Calculator
- Updated
- Formula shown
- Free, no sign-up
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How to use the age calculator
- Enter the date of birth. Most phones and browsers show a date picker; you can also type the date.
- Leave "Age on this date" as today, or set any other date, for example the start of a school year or the day a policy begins.
- If the birthday is February 29, choose whether it counts on February 28 or March 1 in other years.
- Read the age in years, months and days, and the totals underneath. Copy the link to share the same dates.
How age is calculated
Years = ⌊completed months ÷ 12⌋ · Months = completed months mod 12
Days = as-of date − (birth date + completed months)
Total days = as-of date − birth date
This is the anniversary method most people use without thinking about it. Count how many monthly anniversaries of the birth date have passed (Y₁ and M₁ are the birth year and month, Y₂ and M₂ those of the as-of date), split them into years and months, then count the days since the last one. Adding the result back to the birth date always lands exactly on the as-of date, so the answer can be checked by hand.
Total days are the plain calendar difference, with every leap day included. Weeks are total days divided by 7 with the remainder shown, and hours are days × 24 counted from midnight, because the time of birth isn't known. Dates use the Gregorian calendar throughout.
Worked example
Someone born on Tuesday, May 15, 1990 wants their age on Monday, October 19, 2026. From May 1990 to October 2026 is 36 years and 5 months, or 437 months, and the 15th has already passed in October, so all of them count. October 15, 2026 is the last monthly anniversary, and 4 more days reach the 19th. The age is 36 years, 5 months and 4 days.
In total that is 13,306 days (1,900 weeks and 6 days), or about 319,344 hours. They were born on a Tuesday, and their next birthday, turning 37, is Saturday, May 15, 2027: 208 days away.
Days old at milestone birthdays
The number of days in a span of years depends on how many February 29ths it contains. This table was generated with the calculator's engine for birthdays in every year from 1940 to 2010, so it shows the range you could see.
| Birthday | Days old | Weeks (approx.) |
|---|---|---|
| 1st | 365 or 366 | 52 |
| 10th | 3,652 or 3,653 | 521 |
| 13th | 4,748 or 4,749 | 678 |
| 16th | 5,844 | 834 |
| 18th | 6,574 or 6,575 | 939 |
| 21st | 7,670 or 7,671 | 1,095 |
| 30th | 10,957 or 10,958 | 1,565 |
| 40th | 14,610 | 2,087 |
| 50th | 18,262 or 18,263 | 2,608 |
| 65th | 23,741 or 23,742 | 3,391 |
| 80th | 29,220 | 4,174 |
| 100th | 36,524 or 36,525 | 5,217 |
Leap-day birthdays
A person born on February 29 has a real birthday only once every four years, apart from century years such as 2100 that skip the leap day. In the years between, families and organizations pick either February 28 or March 1. This calculator defaults to February 28, the same "last day of the month" rule it uses for anyone born on the 29th, 30th or 31st, and lets you switch. For someone born on February 29, 2000:
| Year | February 28 rule | March 1 rule |
|---|---|---|
| 2025 | Fri, Feb 28, 2025 | Sat, Mar 1, 2025 |
| 2026 | Sat, Feb 28, 2026 | Sun, Mar 1, 2026 |
| 2027 | Sun, Feb 28, 2027 | Mon, Mar 1, 2027 |
| 2028 | Tue, Feb 29, 2028 | Same (leap year) |
| 2029 | Wed, Feb 28, 2029 | Thu, Mar 1, 2029 |
| 2030 | Thu, Feb 28, 2030 | Fri, Mar 1, 2030 |
| 2031 | Fri, Feb 28, 2031 | Sat, Mar 1, 2031 |
| 2032 | Sun, Feb 29, 2032 | Same (leap year) |
Some laws set their own rule for when a leap-day baby reaches an age such as 18 or 21. If the exact day matters for something official, check the rule that applies where you live.
Tips for accurate ages
- Ages are counted, not rounded. You turn 18 on your 18th birthday, not when you are "nearly" 18, so the years figure only goes up on the birthday itself.
- Months vary in length. "6 months old" means six monthly anniversaries have passed, which can be anywhere from 181 to 184 days. Use the total days when you need a fixed count.
- Check the "age on" date for forms. School entry, sports leagues and insurance often ask for age on a cut-off date, not today. Enter that date instead.
- This uses international age. You are 0 at birth and add a year on each birthday. Some traditional East Asian systems count age differently.
To count the days between any two dates, use the day counter; to add months or years to a date, the date calculator; and to see which weekday a date falls on, the day of the week calculator.
Frequently asked questions
How is age calculated in years, months and days?
Count the whole years to the most recent birthday, then the whole months since that birthday, then the days left over. Someone born on May 15, 1990 is 36 years, 5 months and 4 days old on October 19, 2026: 36 birthdays have passed, 5 more monthly anniversaries (June 15 to October 15), and 4 days since October 15.
How many days old am I?
Subtract the two dates as calendar days. For a May 15, 1990 birthday, October 19, 2026 is day 13,306, which is 1,900 weeks and 6 days, or 437 whole months and 4 days. The total includes every leap day in between, so two people of the same age in years can differ by a day.
When does someone born on February 29 have a birthday?
In leap years, on February 29. In other years this calculator uses February 28 by default, and you can switch to March 1. On February 28, 2025, a person born on February 29, 2000 is 25 under the February 28 rule, or 24 years, 11 months and 30 days under the March 1 rule.
Why does a January 31 birthday reach one month on February 28?
February has no 31st, so the monthly anniversary moves to the last day of the month. A baby born on January 31, 2026 is 1 month old on February 28, 2026, and 1 month and 1 day old on March 1. The same month-end rule is used when you add months in the date calculator.
Does the calculator use my time of birth or time zone?
No. It counts whole calendar days between the two dates, so the result is the same wherever you are. Age in hours is the number of days multiplied by 24, from midnight to midnight. "Today" is your device's current date, which you can change.