Chronological Age Calculator

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The Chronological Age Calculator on this page will subtract a date of birth from a test date and show its work.

This date calculator will calculate the age of a person on a given test date in years, months, and days, and then show its work so you can perform the subtraction manually when you don't have access to the calculator.

Plus, the calculator will also tell you a person's age rounded to the nearest month, and from there convert the years and months into their age in total number of months.

Note that if you would like a more precise measurement of a person's age, please visit the Age Calculator which converts the number of milliseconds between two dates into years, months, weeks, hours, minutes, and seconds.

How to Manually Subtract One Date From Another

For times when you don't have access to a calculator like the one on this page, the following example illustrates how to figure a person's age in years, months, and days using simple subtraction (actual results from calculator).

For our example, suppose the person/student being tested was born on November 30, 1996, and the date the test is being administered is August 7, 2013.

To arrive at the chronological age, we first set up a subtraction problem, where we will subtract the birth date from the test date. Here is how our initial subtraction problem is laid out:

Date Years Months Days
Test 2013 8 7
Birth 1996 11 30

Step #1: As with any other subtraction problem, we start subtracting in the right-most column -- which in this case is the "Days" column:

Date Years Months Days
Test 2013 7 8 37 7
Birth 1996 11 30
= Age     7

Since 7 days in the Test row is less than 30 days in the Birth row, we need to borrow 30 days (1 month) from the Test/Months cell, which leaves us with 7 months in the Test/Months cell and 37 days in the Test/Days cell. Subtracting 30 days from 37 days gives us a result of 7 days in the Age/Days cell.

Step #2: Next we move to the Months column:

Date Years Months Days
Test 2012 2013 19 7 37
Birth 1996 11 30
= Age   8 7

Since 7 months in the Test row is less than 11 months in the Birth row, we need to borrow 12 months (1 year) from the Test/Years cell, which leaves us with 2012 years in the Test/Years cell and 19 months in the Test/Months cell. Subtracting 11 months from 19 months gives us a result of 8 months in the Age/Months cell.

Step #3: Lastly, we perform the subtraction in the Years column:

Date Years Months Days
Test 2012 19 37
Birth 1996 11 30
= Age 16 8 7

Subtracting 1996 years from 2012 years gives us a result of 16 years in the Age/Years cell. Therefore, subtracting the birth date from the test date gives us a chronological age of 16 years, 8 months, and 7 days

Note that I intentionally used two dates that would require borrowing from one column to supplement another so you could see how the borrowing works when subtracting dates. In cases where the top number (test months or days) is greater than the bottom number (birth months or days) you would simply subtract the bottom number from the top number.

With that, let's use the following calculator to subtract a date of birth from a test date.

Chronological Age Calculator
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Instructions: Select the month, day and year of the desired test date.

Next, select the month, day, and year of the birth date for the person being tested, and then click the "Calculate Chronological Age and Show Work" button.

Mouse over the blue question marks for a further explanation of each entry field. More in-depth explanations can be found in the glossary of terms located beneath the Chronological Age Calculator.

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Help Test date:
Help Birth date:
Help Chronological age:
Help Rounded to nearest month:
Help Age in months:
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Chronological Age Calculator Glossary of Terms

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Test date: Select the month, day, and year of the test date.

Birth date: Select the month, day, and year of the date of birth of the person being tested.

Chronological age: This is the result of manually subtracting the entered date of birth from the entered test date.

Age rounded to nearest month: This is the calculated chronological age rounded to the nearest month.

Age in months: This is the calculated chronological age converted into total number of months (from rounded result).

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