Chronological Age Calculator with Built-in Dynamic Tutorial

Chronological Age Calculator Sign

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 calculate age 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 the 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.

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Chronological Age Calculator

Subtract date of birth from test date and see how to calculate chronological age by hand.

Special Instructions

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Selected Data Record:

A Data Record is a set of calculator entries that are stored in your web browser's Local Storage. If a Data Record is currently selected in the "Data" tab, this line will list the name you gave to that data record. If no data record is selected, or you have no entries stored for this calculator, the line will display "None".

DataData recordData recordSelected data record: None
Test date:

Test date:

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

Birth date:

Ending date:

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

Chrono age:Chronological age:Chronological age:Chronological age:

Chronological age:

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

Nearest month:Nearest month:Rounded to nearest month:Rounded to nearest month:

Rounded to nearest month:

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

Age in months:Age in months:Chronological age in months:Chronological age in months:

Chronological age in months:

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

If you would like to save the current entries to the secure online database, tap or click on the Data tab, select "New Data Record", give the data record a name, then tap or click the Save button. To save changes to previously saved entries, simply tap the Save button. Please select and "Clear" any data records you no longer need.

Help and Tools


What chronological age is and how to manually subtract one date from another.

What is a Chronological Age

Unlike biological age, which refers to how old you appear to be, chronological age is how long you have been alive, expressed in the number of years, months, and days.

For example, if you were born on October 5, 1996, your chronological age as of June 20, 2019 would be 22 years, 8 months, and 15 days.

How to Calculate Chronological Age by Hand

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 (chronological age formula used by the 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:


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

 Test20137 837 7
=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:

 Test2012 201319 737
=Age 87

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:


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.

Taking the age calculation one step further, you can calculate the chronological age in months by rounding to the nearest month (16 years, 8 months, and 7 days rounded to 16 years, 8 months), convert the years to months (16 years x 12 = 192 months) and total the months (192 + 8 = 200 months).

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.

Adjust Calculator Width:

Move the slider to left and right to adjust the calculator width. Note that the Help and Tools panel will be hidden when the calculator is too wide to fit both on the screen. Moving the slider to the left will bring the instructions and tools panel back into view.

Also note that some calculators will reformat to accommodate the screen size as you make the calculator wider or narrower. If the calculator is narrow, columns of entry rows will be converted to a vertical entry form, whereas a wider calculator will display columns of entry rows, and the entry fields will be smaller in size ... since they will not need to be "thumb friendly".

Show/Hide Popup Keypads:

Select Show or Hide to show or hide the popup keypad icons located next to numeric entry fields. These are generally only needed for mobile devices that don't have decimal points in their numeric keypads. So if you are on a desktop, you may find the calculator to be more user-friendly and less cluttered without them.

Stick/Unstick Tools:

Select Stick or Unstick to stick or unstick the help and tools panel. Selecting "Stick" will keep the panel in view while scrolling the calculator vertically. If you find that annoying, select "Unstick" to keep the panel in a stationary position.

If the tools panel becomes "Unstuck" on its own, try clicking "Unstick" and then "Stick" to re-stick the panel.