How is a golf handicap calculated?
A handicap index is the average of your best eight score differentials from your most recent twenty rounds. Each differential adjusts your score for how hard the course played, using the formula (113 ÷ slope rating) × (your adjusted score − course rating).
Your score alone is not enough
Shooting 88 on a short, flat course in still air is not the same performance as shooting 88 into a wind on a long one. A handicap that averaged raw scores would reward playing easy courses, so every score is converted into a *differential* first.
Two published numbers do that work. The course rating is what a scratch golfer is expected to shoot — often not the same as par. The slope rating, from 55 to 155, describes how much harder the course gets for everyone else, with 113 as the neutral middle.
The differential
Each round becomes one number:
| Score differential | (113 ÷ slope) × (adjusted gross score − course rating) |
Example: an 88 on a course rated 70.4 with a slope of 125 gives (113 ÷ 125) × (88 − 70.4) = 15.9.
Best eight of twenty
Your index is not the average of your rounds — it is the average of your *best* rounds. The most recent twenty differentials are taken, the lowest eight of those are averaged, and that is your index.
It is therefore a measure of what you are capable of rather than what you typically shoot. Most golfers play to their handicap far less often than they expect to, and that is by design rather than a fault.
- Twenty rounds go into the pool, and the oldest drops out as each new one lands
- The best eight of those twenty are averaged
- A round that was never one of your best eight has no effect on your index at all
What The Caddy calculates
The app computes a WHS-style index from the rounds you score in it, using the differential formula above and the best eight of your last twenty. It needs at least three rounds with a rating and slope before it will show you anything.
Two things to be clear about. It applies a 0.96 factor to the average, and rounds it to one decimal place. And it is not an official handicap — only your club and national association can issue one of those. It is a like-for-like measure of your own game, computed from your own cards.
Rounds played on a course with no scorecard on file are excluded outright. Those are scored against a guessed par, and a handicap built on a guess is worse than no handicap, because it looks authoritative.
Index against course handicap
Your index is portable — it travels with you. It is not the number of strokes you receive on the day.
That figure, the course handicap, is worked out from your index against the specific tee you are playing: your index, scaled by the slope of that tee, then adjusted for the gap between its course rating and its par. Playing further back gives you more strokes for the same index, which is exactly right.
Common questions
How many rounds do I need for a handicap?
Officially, 54 holes — three 18-hole rounds. The Caddy uses the same threshold and shows no index until it holds three qualifying rounds.
Is the handicap in The Caddy an official handicap?
No. It is a WHS-style index computed from the rounds you score in the app. Only your club and national association can issue an official one.
Why did a bad round not change my handicap?
Because your index only averages your best eight differentials of the last twenty. A round outside that eight has no effect — it only matters once it displaces one of them, or once better rounds age out.
What is a slope rating?
A number from 55 to 155 describing how much harder a course plays for a bogey golfer than for a scratch one. 113 is the neutral value, which is why it appears in the differential formula.
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