Calculating someone’s age in Excel should be pretty straightforward. You would think there was an Age() function in Excel, but unfortunately, we’re on our own to figure this one out. No worries, though, it’s not as bad as you might think.

Let’s get started.

# The Problem

Say you have someone’s birthdate such as `4/4/1988`

. How would you go about calculating their age?

You might say something like “easy, just take today’s date and subtract the birthdate.” Well, that’s a good starting point. Let’s work with that.

Assuming the birthdate is in `A1`

, we’ll take today’s date (using the `TODAY()`

function) and subtract the birthdate:

=TODAY()-$A$1 =5/5/29 (May 5th, 1929)

The result is May 5th, 1929? How did that happen?

# How dates work in Excel

It’s important to take a second to explain how dates work in Excel. Put the number `1`

in a cell and convert it to a date. It will display `1/1/1900`

. This is because dates in Excel start from `1/1/1900`

. If you changed the cell by putting a `2`

in there, the date would become `1/2/1900`

. What this means is that each number represents how many days it has been since `1/1/1900`

.

Let’s look at the formula when we convert the dates into numbers.

=TODAY()-$A$1 =8/8/2017 - 4/4/1988 =42955 - 32237 =10718

If you put the number `10718`

in a cell and format it as a date you’d get `5/5/29`

.

But what does the number `10718`

represent, anyway?

It actually represents the number of days between `4/4/1988`

and `8/8/2017`

(including leap days). So this person who has a birthdate of `4/4/1988`

has lived for `10,718`

days. We can use this to figure out how many years they are. We just need to divide by `365.25`

(days in a year – including the fraction for leap years).

# Calculating Someone’s Age the Right Way

Let’s adjust the formula slightly

=(TODAY()-$A$1)/365.25 =29.3442847

This person is `29`

years old. The fraction portion represents how much of a percentage of a new year they have lived. In our formula, this would be `~34%`

of a new year, which translates to about `4`

months. So `29`

years and `4`

months of age.

From here, we can either fix the number format to not include fractions or adjust the formula one last time:

`=ROUND((TODAY()-$A$1)/365.25,0)`

And that’s how you calculate someone’s age in Excel.