capping cell value

I am horrible at using excel. How do I get a cell to return a value no more than 100%.
I have a simple function: =SUM(AF20/12). Once AF20 reaches 12 100% is displayed in AH20. I am tracking a required 12 hours of training, but want to show on my document all classes performed. I just want AH20 to show 100% when I hit 12 hours then stop!

Or

=MIN(AF20,12)/12