Your golf handicap index allows you to fairly compete with players of all skill levels by allowing you a specific number of extra strokes on an 18-hole golf course. Because of time constraints, you may prefer to play 9-hole rounds. If that's the case, you should calculate your 9-hole handicap index as well. Figuring out the 9-hole handicap differentials used to calculate your index involves making a simple adjustment to the 18-hole handicap differential formula: You divide course ratings by 2.
Calculating a 9-Hole Handicap Differential
Play a 9-hole round of golf and write down your score.
Calculate the adjusted course rating by dividing the given course rating by 2. This applies only to 18-hole courses. If you have played a 9-hole course, you will not need to adjust the course rating.
For example, imagine you played 9 holes on an 18-hole course with a rating of 72.3. The adjusted course rating would be 72.3 divided by 2, or 36.2.
Plug the results from Steps 1 and 2 into the following formula for your handicap differential:
Handicap Differential = (Score - Adjusted Course Rating) x (113 / Course Slope).
The calculation would look like this on a course with a slope of 120:
Handicap Differential = (44 - 36.2) x (113 / 120) = 7.3.
Add an "N" to the differential calculation to indicate that it is a 9-hole handicap: 7.3N.
Calculating a 9-Hole Handicap Index
Write down the best five of your latest 9-hole handicap differentials. The Professional Golf Association recommends calculating your handicap index based on 20 scores, but will accept indexes calculated from five. For example, imagine that your best five differentials lately have been 7.5N, 8.0N, 7.3N, 7.9N and 7.8N.
Average the five differentials. In the example, the calculation would look like this:
Average = (7.5N + 8.0N + 7.3N + 7.9N + 7.8N) / 5 = 7.7N.
Multiply the average by 0.96 to obtain your 9-hole handicap index. In the example, the calculation would look like this:
Handicap Index = 0.96 x 7.7N = 7.4N.