This calculator does two jobs built on the World Handicap System (WHS). First it turns a single round into a score differential from your adjusted gross score, course rating and slope rating. Then it averages a set of your differentials into a Handicap Index — the portable number that travels with you between courses.
How it works
For one round, the score differential is:
Score Differential = (113 ÷ Slope Rating) × (Adjusted Gross Score − Course Rating)
The constant 113 is the slope of a course of standard difficulty, so this normalises every round to a common scale.
Your Handicap Index is the average of your lowest differentials, but how many count depends on how many scores you have entered. The tool sorts your differentials and averages the best ones per the WHS table:
| Scores entered | Lowest differentials used |
|---|---|
| 3 | 1 |
| 6 | 2 |
| 9–11 | 3 |
| 12–14 | 4 |
| 15–16 | 5 |
| 17–18 | 6 |
| 19 | 7 |
| 20+ | 8 |
Example
You shoot an adjusted gross score of 85 on a course rated 71.2 with a slope of 128:
Differential = (113 ÷ 128) × (85 − 71.2) = 0.8828 × 13.8 = 12.2
Enter a set such as 18.2, 15.6, 21.0, 14.8, 19.5, 16.1, 17.7, 20.3 (8 scores). The tool sorts them and averages the lowest 2 — 14.8 and 15.6 — for a Handicap Index of about 15.2.
Everything runs in your browser — your scores never leave your device.