James A. wrote:
Let's say column A is my project start date and column B is my project finish
date. I have my formula which calculates how many days it took me to
complete each project which ranges anywhere from 1 day to 7 days. I had 20
projects last month and my contract is to complete each project within 3
days.

I need excel to calculate how many projects were completed within 3 days and
the total percentage.

Any help is greatly appreciated!

=COUNTIF(A1:A20,"<4")/COUNT(A1:A20) and format the result as a percent.
this assumes you have 20 entries for projects in A1:A20