Golf Digest, May, 2008
Q: What is a "Handicap Differential" and how is it used?
A: The arithmetic used in the USGA Handicap System comes in when the golf club calculates a player’s Differential for each score he posts. The Differential is the difference between a player’s adjusted gross score and the USGA Course Rating of the course on which the score was made, multiplied by 113, and then the total is divided by the USGA Slope Rating from the tees played rounded off to one decimal place. For example, if you post an 80 on a course with a Course Rating of 68.7 and a Slope Rating of 105, your Handicap Differential is 12.2. The next step entails averaging your best 10 Handicap Differentials, which your golf club or association then will multiply by a 96-percent "bonus for excellence" factor that slightly favors the lower-handicap player. The next step is to delete all numbers after the first decimal digit, with no rounding off to the nearest tenth. Your club Handicap Committee then reviews your record, modifies it, if necessary and then issues your USGA Handicap Index.
By Dean Knuth, Golf Digest Professional Advisor. Former senior director of the USGA handicap department, Knuth invented today's USGA Course Rating and Slope system.