Look up your golf scores, USGA Course and Slope Ratings for the last 20 rounds of golf you played. While you can calculate your handicap with fewer scores, the handicap is most accurate with more scores.
Subtract the USGA course rating for the course from your score, multiply the result by 113 and divide the result by the Slope Rating to calculate your handicap differential for each round you played. For example, if you shot an 82 on a course with 71 Course Rating and a 115 Slope Rating, you would subtract 71 from 82 to get 11, multiply 11 by 113 to get 1243, and divide 1243 by 115 to get 10.808696.
Select the 10 lowest handicap differentials from your most recent 20 rounds of golf.
Compute the average of your 10 best handicap differentials by adding them and dividing by 10.
Multiply the average of your handicap differentials by 0.96. For example, if your average equals 11.35, you would multiply 11.35 by 0.96 to get 10.896.
Delete, not round, all numbers after the tenths digit to find your USGA handicap. Finishing the example, you would drop all number after the tenths place in 10.896 to find your handicap to be 10.8.