Age Calculator

How old am I? Find your age from your date of birth

Enter your date of birth and the date you want your age on, and the calculator shows your exact age in completed years, months and days, updated as you type. Under it are your age in months, weeks and days, your next birthday with its weekday and a countdown in days, and the day of the week you were born.

• What you know: choose Full date of birth for an exact age, or Year of birth only when you know just the year (see below).
• Date of birth: type it or pick it from the calendar. Any date from the year 1 to 9999 works.
• Age on date: the date you want the age on. The page opens on the example’s date; press Use today’s date under the result to switch to today on your device. Past and future dates work too: a school cutoff, a job application deadline or a day decades ahead.
• Leap-day birthday counts on (shown only for a February 29 birth): February 28 or March 1 in years without a February 29, explained below.

The Try buttons load a February 29 birthday in a common year, a baby born January 31 on February 28, the day of an 18th birthday, the age on January 1, 2030, and a birth year alone (1998). To see the age on several dates, press Save for comparison, change the age-on date and save again: up to three dates sit side by side, each showing how many days it adds to the first. Continue in the Countdown to a Date opens a live countdown to the next birthday.

For the time between two dates that aren’t a birth date, such as the days until a deadline, the Days Between Dates Calculator counts it, with an option to include the end date. To find the date you will be any number of days old, add that many days to your date of birth in the Add or Subtract Dates Calculator.

How is age calculated in years, months and days?

Age counts forward from the date of birth in three steps: whole years to the last birthday, then whole months after it, then the days left over.

1. Years: if this year’s birthday has come by the age-on date, the age is the age-on year minus the birth year; if not, one year less.
2. Months: from the last birthday, count the month marks (the same day of the month as the birth) that have passed.
3. Days: count the days from the last month mark to the age-on date.

On a birthday the months and days are both 0, and the new year of age counts from the start of that day: 18th birthday loads someone born on September 23, 2008, who is 18 years, 0 months, 0 days old on September 23, 2026.

The totals come from the same count. The age in days is the number of days from the date of birth to the age-on date, so a baby is 0 days old on the day it is born and 1 day old the next day.

$$\text{age in months} = 12 \times \text{years} + \text{months}, \qquad \text{weeks} = \left\lfloor \frac{\text{days old}}{7} \right\rfloor$$

Worked example: born March 30, 1991, age on September 23, 2026

1. Completed years: the 2026 birthday, March 30, 2026, is on or before September 23, 2026, so the age is 2026 − 1991 = 35 years.
2. Whole months: from March 30, 2026 to August 30, 2026 is 5 months. The next month mark, September 30, is after September 23.
3. Days left over: August 30 to September 23 is 24 days (1 day to August 31, then 23).
4. Age: 35 years, 5 months, 24 days, written 35;5;24.
5. Totals: September 23, 2026 is 12,961 days after March 30, 1991, which is 1,851 weeks and 4 days. In months: 35 × 12 + 5 = 425 months and 24 days.
6. Next birthday: Tuesday, March 30, 2027, 188 days later, when the age turns 36. March 30, 1991 was a Saturday.

How many days, weeks or months old am I?

The Age in days tile answers it directly: 12,961 days in the example. Weeks are whole 7-day weeks plus the days left (1,851 weeks and 4 days), and months are calendar months plus days (425 months and 24 days). Hours are the days times 24, so 311,064 hours in the example; the time of birth isn’t counted.

The Birthdays and day-count milestones table lists the dates of round birthdays and of being 1,000, 5,000, 10,000, 20,000 and 30,000 days old, each with its weekday and how many days it is from the age-on date. The example person was 10,000 days old on Wednesday, August 15, 2018, and turns 40 on Sunday, March 30, 2031, in 1,649 days. Download the table as a CSV file to keep the dates.

How old was I, or will I be, on another date?

Change the age-on date. Press On Jan 1, 2030, for example: the person born on March 30, 1991 will be 38 years, 9 months, 2 days old on January 1, 2030, with the 39th birthday 88 days later.

The Age on September 23 in other years table answers the same question for a run of years: a few either side of your date, then each round decade ahead. The months and days usually stay the same from year to year, so the years column is the quick answer to “how old will I be in 2040?”. On September 23, 2040, the example person is 49 years, 5 months, 24 days old, or 18,075 days.

How old am I if I only know my birth year?

Your age is one of two numbers, depending on whether your birthday has come yet this year. Choose Year of birth only: for someone born in 1998, on September 23, 2026 the age is 2026 − 1998 = 28 if the birthday falls on or before September 23, and 27 if it comes later in the year. On December 31 every birthday of the year has passed, so the answer is a single age. For months and days, you need the full date of birth.

Born on February 29: when does a leap-day baby turn a year older?

In a leap year, on February 29. In the other years there is no February 29, so the birthday has to count on another day, and two rules are in use:

• February 28: the last day of February stands in for the missing 29th. This is what date software such as Java’s LocalDate does when it adds whole years to February 29.
• March 1: the birthday counts on March 1, the day after February 28. Hong Kong’s age-of-majority law, for example, takes March 1 as the anniversary in years that aren’t leap years.

The calculator asks which rule to use and shows what the other rule gives. Press Feb 29 birthday: for someone born on February 29, 2004, on February 28, 2025 the age is exactly 21 years, 0 months, 0 days under the February 28 rule. Under the March 1 rule the same date is 20 years, 11 months, 30 days, and the 21st birthday is the next day, Saturday, March 1, 2025. Either way, exactly one day in 2025 shows the age as 21 years, 0 months, 0 days.

If a legal or official age depends on it, use the rule that applies to you; this page doesn’t decide it. Century years matter too: 1900 was not a leap year and 2000 was, so someone born on February 29, 1896 had no February 29 birthday until 1904.

Why age calculators can disagree by a day

Methods differ mainly at month ends. Someone born on January 31 has no “31st” to reach in February. This calculator, like date software that moves a missing day to the month’s last day, counts February 28 as the 1-month mark: born January 31, 2026, the age on February 28, 2026 is 0 years, 1 month, 0 days, and on March 1 it is 1 month, 1 day. A method that waits for a 31st shows 0 months, 28 days on February 28 instead. Both are 28 days old; they only name it differently. For a birth on the 1st to the 28th, every month has that day, so this question never comes up.

The other causes are the February 29 rule above and “today”. The Use today’s date button takes the date from your device, so it matches the calendar where you are. The time of birth isn’t used: a person born late in the evening turns a year older on the same calendar date as one born just after midnight.

Calculating age in Excel or Google Sheets

With the date of birth in cell A1 and the age-on date in B1:

• =DATEDIF(A1,B1,"Y") gives the completed years: 35 in the example.
• =DATEDIF(A1,B1,"YM") gives the whole months after them: 5.
• =B1-A1 gives the age in days: 12,961.

These match the calculator for dates from March 1900 on, unless a month end or February 29 moved the last birthday or month mark; the How this was calculated steps show the formulas with your own results whenever they apply. Avoid "MD" for the days: Microsoft’s own documentation warns that DATEDIF can give incorrect results in some cases and recommends against that unit. When a month end or February 29 is involved, check a spreadsheet’s answer against the steps here.

Reading the result

• The headline is the age on the date named above it, with the weekday. Under it, a line says whether that date is today on your device and offers Use today’s date when it isn’t.
• Next birthday in counts the days to the next birthday and names its date, weekday and the age reached.
• Age in months, Age in weeks and Age in days are the totals, each with its remainder.
• Born on a is the weekday of the date of birth.
• Chronological age writes the age compactly as years;months;days (35;5;24). It is the plain count; if a test manual or form gives its own rounding rule, follow that rule.
• Born on February 29 (leap-day births only) shows the age and next birthday under the other rule.
• The steps show each date used, including where a month end or a leap day moved a mark.
• The two tables list milestone dates and the age in other years. Both download as CSV files.

Assumptions and limitations

• Dates are counted in the Gregorian calendar, extended backward before its introduction in 1582. A date in an old record written in the Julian calendar needs converting to a Gregorian date first; for dates in 1582 or earlier the result carries a reminder.
• Only calendar dates count. Time of birth and time zones are ignored, and an age changes at the start of the birthday.
• Hours are days × 24, so clock changes for daylight saving time are not counted.
• Age starts at 0 on the date of birth and goes up by one on each birthday.
• Dates from January 1 of the year 1 to December 31, 9999 are accepted; a next birthday after 9999 is not shown.

Common mistakes

• Changing only the date of birth. The age-on date still holds the example’s date until you change it. The page names it in a note above the result and offers Use today’s date.
• Typing a two-digit year. “98” in the year of birth means the year 98. The field says so; type 1998.
• Multiplying years by 365 for days old. Leap days add up: from March 30, 1991 to the 35th birthday is 12,784 days, not 35 × 365 = 12,775.
• Dividing by an average month. 12,961 days ÷ 30.4375 (an average month) is 425.82 “average months”, but the calendar count is 425 months and 24 days.
• Counting the day of birth as day 1. Days old start at 0 on the day of birth. For a count that includes both the birth date and the age-on date, add 1.