Explanation
The goal is to display a checkmark (also called a "tick mark" in British English) when a task is marked complete. The easiest way to do this is with the IF function and the mark you would like to display. The article below explains several options.
IF with a plain checkmark
The simplest approach, and the one that appears in the example shown, is to use a plain text checkmark like this:
=IF(C5="complete","✓","")
This formula uses the IF function to check for "complete" in column C. When the value is "complete", IF returns a checkmark (✓). When the value in column C is anything else, IF returns an empty string (""), which looks like a blank cell in Excel. Notice the checkmark itself must be enclosed in double quotes ("") since it is text.
IF with UNICHAR
A more flexible way to display a checkmark is to use the IF function with the UNICHAR function like this:
=IF(C5="complete",UNICHAR(10003),"")
The logic of this formula is the same as the original formula above. However, instead of hardcoding a plain text version of a checkmark into the formula, the UNICHAR function is used to return the Unicode character 10003. The benefit of this approach is that you can easily change the number to display a different character. Here are a few examples of Unicode characters related to check and tick marks:
To use a different symbol, change the number in the formula. For example, use 10007 for an "X":
=IF(C5="complete",UNICHAR(10007),"")
For more useful Unicode symbols, see: How to use the UNICHAR function.
IF with CHAR
An older way to display a checkmark in a formula is to use IF with the CHAR function, then format the result with the Wingdings font:
=IF(C5="complete",CHAR(252),"")
Note: with this option, you must format the range D4:D12 with the Wingdings font. If you skip this step, you will not see a checkmark. Instead, you will see a character like "ü" or similar.
With conditional formatting
You can also use Excel's built-in conditional formatting icons to show a checkmark, but you don't have much flexibility. Visit this page for a comprehensive guide on conditional formatting with formulas, featuring many practical examples.