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To calculate your Handicap Index, you’ll first need a minimum of five golf scores (and no more than 20).  Gather at least five scores 18-hole scores or ten 9-hole scores and use them to calculate your Adjusted Gross Score. To determine your Adjusted Gross Score (AGS), total up the number of strokes taken during a round, then adjust for the maximum per-hole scores (determined by the USGA’s Equitable Stroke Control guidelines). Most golf courses make the information on maximum per-hole scores available to the general public. Check the course’s website or inquire at the clubhouse. For example, if you took 8 strokes on a hole whose maximum-per hole score is 5, you would count 5 strokes (not 8) for that hole when adding up your total number of strokes for the game. Once you have your AGS, use it to determine your handicap differential.  The equation for a Handicap Differential is the AGS minus Course rating, multiplied by 113, and divided by the Slope Rating, or (AGS - Course Rating) x 113 / Slope Rating. The Course Rating is the numerical value given by the UGSA to each set of tees on a course. It approximates the number of strokes it should take a scratch golfer to complete the course. Most courses make this information available via the course website or at the clubhouse. The Slope Rating shows the difficulty of a course for an average golfer and is calculated by comparing the Course Rating to the scores of bogey golfers. Most golf courses make the Slope Rating available to their guests; again, check their website or at the clubhouse. For example, say your AGS is 85, the Course Rating is 69.3, and the Slope Rating is 117. You would have the equation (AGS - Course Rating) x 113 / Slope Rating, or (85 - 69.3) x 113 / 117, which results in a Handicap Differential of 15.2. The formula for your Handicap Index is the sum of your differentials divided by the number of differentials, multiplied by 0.96, or (Sum of Differentials / Number of Differentials) x 0.96.  The figure of 0.96 in the equation represents the “bonus for excellence” that the UGSA has figured into the Handicap Index. Determine the number of differentials to be used. If you’re using 5-6 scores, use the lowest differential; if you have scores from 7-8 rounds, use the lowest two differentials; if you have scores from 9-10 rounds, use the lowest three differentials; and so on). You can use up to 20 scores (for which you would use the 10 lowest differentials). For more detail on how many differentials to use, see the UGSA Handicap Differentials Chart. For example, if you’re using 8 scores, you’ll be using the lowest two differentials. Let’s say your two lowest differentials are 10 and 11. To average them, add them together, and then divide the resulting number by 2. Then multiply the result by 0.96, and drop any digits beyond the tenths place. The equation would look like this: 10 + 11 = 21; 21 / 2 = 10.5; 10.5 x 0.96 = 10.08. Dropping the digit beyond the tenths place gives you a handicap index of 10.0 (remember not to round up).
Find your adjusted gross score. Calculate your Handicap Differential. Calculate your Handicap Index.