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Subtract course rating from your score, multiply by 113 and divide by slope rating. A score of 90 on a course rated 72 with slope 113 gives a differential of 18.0, which is the building block of a handicap index.
Slope rating adjusts for course difficulty, with 113 as the standard slope. The same score on a harder course, with a higher slope, gives a lower differential than on an easier course.
Course rating estimates what a scratch golfer should shoot from those tees, often near par but sometimes several strokes away. Slope rating measures how much harder the course plays for a bogey golfer than for a scratch golfer, ranging from 55 to 155, with 113 as the standard average. Both numbers come from the scorecard or course website, and both are needed for a differential.
Use adjusted gross score, not raw score. Under the World Handicap System (WHS), the maximum score on a hole is net double bogey: par plus 2 plus any handicap strokes received on that hole. If you card more than that on a hole, record the capped score instead, so one blow-up hole does not inflate your differential.
A handicap index is not one differential. Under WHS it averages the best 8 differentials from your most recent 20 rounds, rounded to one decimal place. With fewer scores the system uses fewer best differentials: lowest 1 from 3 to 5 scores, lowest 2 from 7 scores, lowest 3 from 9 scores, and so on up to 8 from 20. This calculator gives the single-round differential, which is the building block of the index.
Your course handicap for the day converts your index to the tees you play: course handicap = handicap index × (slope rating / 113) + (course rating - par), rounded to a whole number. For example, an index of 13.5 on tees with slope 130, course rating 71.5 and par 72 gives 13.5 × (130 / 113) - 0.5 = 15.03, so 15 strokes for that round.
A golfer shoots an adjusted gross score of 88 on a course rated 72.1 with slope 128. Step one: 88 - 72.1 = 15.9. Step two: 15.9 × 113 = 1796.7. Step three: 1796.7 / 128 = 14.04, which rounds to 14.0 to one decimal place, the usual handicap reporting precision.
With an adjusted gross score of 90, course rating 72.5 and slope 125, the differential is (90 - 72.5) × 113 / 125 = 17.5 × 113 / 125 = 1977.5 / 125 = 15.82. Keep differentials to one decimal place when recording them, even though this calculator shows two decimals for checking.
Entering a raw score instead of an adjusted gross score is the biggest error, since uncapped blow-up holes inflate differentials. Using ratings from the wrong tees, treating one differential as an index, and ignoring slope all distort the result. Always confirm course and slope ratings from the scorecard, and remember this differential is an estimate, not an official WHS index.
It is a single round score adjusted for course rating and slope, so rounds on different courses can be compared fairly. A handicap index is built from your best differentials.
Slope 113 is the standard difficulty for an average course. Higher slope means a harder course for bogey golfers relative to scratch golfers.
Your total score after capping each hole at net double bogey: par plus 2 plus handicap strokes received on that hole. Use adjusted gross score, not raw score, for handicap maths.
The maximum hole score for handicap purposes: par of the hole, plus 2 for double bogey, plus any handicap strokes you receive on that hole. It stops one bad hole from ruining a handicap.
You can get an initial index from 3 eighteen-hole scores, but a full index uses the best 8 differentials from your most recent 20 rounds. More scores make the index more reliable.
No. A differential describes one round. An index averages your best differentials, so it reflects potential ability across many rounds, not a single day.
You can calculate one differential from one round, but not a reliable index. An index needs several rounds, ideally 20, so one great or bad day does not define it.
On the scorecard, the course website, or near the first tee. Make sure the ratings match the exact tees you played, since different tees have different ratings.
113 is the standard slope rating for an average course, used as the baseline. Dividing by the actual slope and multiplying by 113 scales the differential to that standard course.
The playing conditions calculation (PCC) can adjust differentials for unusually hard or easy days, but it is usually zero. This calculator does not apply PCC, so treat its result as the base differential.