Calculators

Time & Date

Calculating the age of a person, place or thing is simply finding the length of time between two dates.

Input the date of birth or start time and the age calculator finds age timespan in years, months, weeks and days.

How This Calculator Calculates Age

This age calculator uses programming language date and time functions to calculate age. The calculator sends user inputs through these functions and calculates the difference between two dates.

The latest update to the age calculator offers the option to calculate date of birth using age on any date. It can also find date of death using age at death so you can measure a person's lifespan. If you know age only in years, or years and months, the calculator finds the date range in which a person was born.

How to Calculate Age

There are two ways to calculate age or date difference if you want to do these calculations by hand.

Method 1: Calculate age in total number of days as the sum of:

• Number of years, x, with 365 days = 365 * x plus,
• Number of leap years, y, with 366 days = 366 * y plus,
• Number of days in the remaining partial year

Your result will be a number of years, plus the number of days in the current partial year.

Method 2: Calculate age, setting up the dates like long subtraction. Put dates in the format yyyy mm dd with the current or more recent date on the top, and the older date on the bottom. Follow these steps and the example to find the difference between two dates as a subtraction problem.

1. Set up the dates like you would set up long subtraction, listing the dates in year, month and day format from left to right.
2. Start all the way on the right and subtract days. You may need to borrow 1 from months. Add the prior month's number of days to the days in the top row, and reduce months by one. So if your date is in April, you'll borrow 31 days from the month of March.
3. Then move one place to the left and subtract months. If necessary, borrow 1 year and add 12 months to the months in the top row. If you do borrow a year, reduce the years by one.
4. Move to the left again and subtract years.
5. The age or date difference result will be in years, months, and days

Example Age Calculation

You want to know the age of a person on March 10, 2026. They were born on November 15, 2006.

Set up the dates like you would set up long subtraction, listing the dates in year, month and day format from left to right.

• Subtract days, 15 from 10. This would result in a negative number so you need to borrow months.
• Borrow 1 from the months column. When you borrow a month, you get the number of days in the previous month, 28 in this case. Going from 3 (March), to 2 (February), move 28 days to the day column and add them to the original 10 days there.
• 10 + 28 = 38
• Then subtract days.
• 38 - 15 = 23

• Subtract months, 11 from 2 is negative.
• Borrow from years. Since all years contain exactly 12 months, simply borrow 1 year from 2026 and add 12 months to the 2 in the top row.
• Then subtract 11 from 14
• 2026 - 1 = 2025
• 2 + 12 = 14
• 14 - 11 = 3

• Finally, subtract years, 2006 from 2025
• 2025 - 2006 = 19

The calculated age, or date difference, is 19 years 3 months 23 days.

See this same math completed by the age calculator: Date difference from November 15, 2006 to March 10, 2026

Date Formats

You can choose which date format you'd like to use for entering your dates in the calculator. Select from month/day/year, day/month/year, or year/month/day.

In the US, dates are typically formatted as month/day/year using a forward slash, a period, or a dash:

• mm/dd/yyyy
• mm.dd.yyyy
• mm-dd-yyyy

In Europe, dates are typically formatted as day/month/year using a forward slash, a period, or a dash:

• dd/mm/yyyy
• dd.mm.yyyy
• dd-mm-yyyy

The international date formatting standard according to ISO 8601 is year-month-day using only a dash (-):

• yyyy-mm-dd

Note that for the age calculator today's date is based on Greenwich Mean Time (GMT).

Notes on Using the Calculator

The age calculator allows you to input single digit days. You do not have to insert a leading zero if the date is less than 10. You must input the 4-digit year.

When counting months and days the calculator uses the actual calendar months across your time calculation. This results in a more accurate months and days calculation compared to using the average month length of 30.42 days (365 ÷ 12 = 30.42).

When counting days, this calculator assumes the start date is day 0 and begins counting after one full day. For example if you input the dates 03/15/2027 and 3/18/2027 into the calculator you will get a total age of 3 days. Day 1 is the 16th, day 2 is the 17th, and day 3 is the 18th. We do not count the 15th because it is day 0.

The calculator automatically accounts for leap years. So within any age calculation it adds one extra day per leap year that occurs in a give time span.

What You Can Do Using the Age Calculator

The age calculator can help you find anyone's age whether they're years old or only weeks old. Answers are listed in multiple units of time including years, months, weeks and days. You can also back-calculate dates of birth or death using known age on a specific date which is helpful when doing geneological research.

What is My Age?

This chronological age calculator can calculate your age. Input your date of birth and today's date to find your current age. You can input a different end date to see what your age would be on that day. The calculator also tells you how many days are left until your next birthday or event date at the bottom of all age calculations.

How Old is My Child?

Parents of newborn babies or infants often need to count weeks or months to tell someone how old their child is. This calculator automatically provides weeks and months of age for any age calculation.

To find how many weeks old your newborn is, input their date of birth and click the Calculate button. The "Find Age on" boxes automatically include today's date but you can also input a date in the future. The calculator displays your child's age in months and weeks, and years if that is the case.

Calculate Date of Birth

If you know someone's age and the date when they were that age, this calculator can find their date of birth. This is helpful for genealogy research when records list a person's age on a census date, marriage record, or other historical document.

Select "Date of Birth" from the Calculate dropdown menu, enter the age in years, months, and/or days, then enter the reference date when the person was that age. Click Calculate to find the date of birth. If you know only the age in years (without months and days), the calculator provides a date range when the person was born.

Calculate Date of Death

This calculator can determine a date of death when you know someone's date of birth and their age at death. This is useful in genealogy to calculate an ancestor's lifespan, or to verify information from documents that list age at death rather than an actual date.

Select "Date of Death" from the Calculate dropdown menu, enter the date of birth and age at death, then click Calculate. If you know only the age in years (without months and days), the calculator provides a date range during which death occurred.

How Many Days Until...?

If you want to calculate by hand how many days until some date or event, you need to account for extra days in leap years. You also need to know the months with 31 days, 30 days, and the one month with 28 days.

Number of Days per Month

• January - 31 days
• February - 28 days in a regular year
• February - 29 days in a leap year
• March - 31 days
• April - 30 days
• May - 31 days
• June - 30 days
• July - 31 days
• August - 31 days
• September - 30 days
• October - 31 days
• November - 30 days
• December - 31 days

You can use the number of days per month list to count the days until a special day like a birthday, holiday, or the start of your vacation. Assuming the date is less than a year away, tally up the number of days per full month between now and your target date. Then add the partial months -- the number of days left in this month, and the number of days in the partial month before your target date.

You also can use the age calculator to find the number of days until an event date. Insert today's date in the "Date of Birth" field, and your target date on "Find Age on" field. The calculator will compute the number of days till your date and display it in the exact number of days.

How to Calculate Age from Birthdate in Excel Spreadsheets

You can use Excel to keep track of age or time since a date or event. To find the number of years since a date of birth or event, input the month, day and year in a cell in Excel in MM/DD/YYYY format. Use the formula =DATEDIF(A1, TODAY(), "Y") to get age in number of years. In the formula, A1 refers to the cell that contains your date of birth or event.

If you need the number of months and days since the date of birth, use this formula in another cell: =DATEDIF(A1, TODAY(), "YM"). This will give you the full months. Finally, in another cell, type =DATEDIF(A1,TODAY(),"MD") to find the remaining days since the date of birth or event.

You can use the "CONCAT" function to string your results together like this: =CONCAT(A2, " years, ", A3, " months, ", A4, " days "). Here, A2, A3 and A4 refer to your outputs years, months, and days respectively.