rules explainer
What a Handicap Index calculation does and leaves out
Work through a Score Differential and the best-8-of-20 average, while keeping the WHS safeguards and official scoring record in view.
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One round becomes a Score Differential
For an 18-hole score, the USGA formula is (113 ÷ Slope Rating) × (Adjusted Gross Score − Course Rating − PCC adjustment). For an adjusted gross score of 90, Course Rating 72.0, Slope Rating 130, and PCC 0, the unrounded result is 15.646 and the Score Differential rounds to 15.6.
Course Rating represents expected performance for a scratch player; Slope Rating expresses relative difficulty for other players compared with a standard Slope of 113. PCC is a daily playing-conditions adjustment supplied by the authorized system, not a number the player guesses.
Twenty scores become an index
With at least 20 Score Differentials, Rule 5.2b averages the lowest eight of the most recent 20 and rounds to the nearest tenth. If those eight are 8.2, 9.1, 9.4, 10.0, 10.3, 10.7, 11.0, and 11.3, the average is 10.0.
That average may still be adjusted. The official record can apply exceptional-score reductions, committee review, and soft or hard caps based on the Low Handicap Index. With fewer than 20 scores, Rule 5.2a uses a smaller number and may apply an adjustment; an index can be established with three 18-hole Score Differentials.
Use the authorized record for the official number
A hand calculation is useful for understanding the system and checking inputs. It cannot reproduce information you do not have, including PCC, expected-score treatment of nine-hole scores, committee adjustments, or the Low Handicap Index safeguards. Post acceptable scores promptly and use the authorized golf association's record for the issued Handicap Index.
Limits
This explainer illustrates USGA-administered World Handicap System rules checked on 2026-09-07. It does not issue an official Handicap Index and may not cover another jurisdiction's administration or future rules revisions.
Sources
- USGA — What is a Score Differential?
- USGA Rule 5.2b — For 20 Scores
- USGA Rule 5.2a — For Fewer Than 20 Scores
- USGA — Handicap Index Calculation
The source-check date records editorial review. Routine builds do not advance it.
Revision history
- — Initial explainer published after checking the current USGA Rules of Handicapping pages.