Partially Blocking Social Security Numbers

If you have a worksheet that includes Social Security Numbers in it, you may be looking for a way to protect the numbers by only displaying the last four digits. So, instead of displaying 278-43-6128, you would only want to display ***-**-6128.

The way to accomplish this depends, in large part, on whether the Social Security Number is stored in the cell as a number or as text. If the SSN is entered with its dashes (as in 278-43-6128), then Excel stores it as text. If the SSN is entered without dashes (as in 278436128), then Excel stores it as a number.

If the SSN is stored as a number, you may be tempted to create a custom format that hides the first part of the number. Unfortunately, there is no way to do this with a custom format. You could create a custom format that would hide all except the first digits, as in this manner:

000,,"-**-****"

As you can surmise from this example, custom formats don't allow you to mask out anything except the last portion of any value. Another drawback to this approach, however, is that Excel "rounds" the SSN, such that 278436128 is displayed as 278-**-****.

The best solution to displaying only the last part of a Social Security Number is to use a second column for the actual display. Instead of trying to format the number (or text) itself, it is best to use a formula that refers to the number and creates the desired result. For instance, if the SSN is in cell B7, then you would place the following formula in a different cell:

="***-****-" & RIGHT(B7,4)

This formula will work with any SSN, regardless of whether it is stored as a number or as text. The other big benefit to this approach is that it allows you to completely hide the original numbers. Even if you were able to use a custom format to hide the first portion of the number (which you can't), someone could still see the SSN in the Formula bar if the cell containing the number is selected.

Using the formula approach, however, allows you to hide the source column, or use sheet protection to hide the contents of the column. This is a big benefit if your goal is to really protect the Social Security Number from prying eyes.