ReckonBoxFrom your Index to strokes on the card
A course handicap is the number of strokes the World Handicap System gives you on a specific set of tees, worked out from your Handicap Index and how hard those tees play. On a slope 125, rating 71.5, par 72 course, an 18.0 Index becomes a Course Handicap of 19.
Your Handicap Index travels with you; the Course Handicap is what you actually use on the day. The formula is Handicap Index times Slope Rating over 113, plus Course Rating minus Par. That last term is the piece that trips up older calculators, and it can move the answer by several strokes.
The formula, in full
Course Handicap equals Handicap Index times (Slope Rating divided by 113), plus (Course Rating minus Par). Two parts, added together.
The first part scales your Index to the tee's difficulty. The 113 is the standard slope, the difficulty of a course of average relative challenge, and the scale runs 55 to 155, so a tee harder than 113 pushes your strokes up. For the 18.0 example, 18 times 125 over 113 is 19.9. The second part adjusts for a course whose rating differs from its par: 71.5 minus 72 is minus 0.5. Add them, 19.9 minus 0.5, and round to 19. On a course rated 75 at par 72, that second term alone adds three strokes.
Why the rating minus par term matters
Before 2020, a course handicap was just Handicap Index times Slope over 113, and plenty of calculators still stop there. The World Handicap System added the Course Rating minus Par term so the number reflects a course that is genuinely harder or easier than its par suggests. Skip it on a tough championship tee rated 75 against a par of 72, and you would be handed three fewer strokes than the system intends. This tool shows the two parts separately, so you can see exactly what the adjustment is doing.
How your Index is built in the first place
Your Handicap Index is the average of your best 8 Score Differentials from your most recent 20 rounds, rounded to one decimal. Each round becomes a Score Differential of 113 divided by the Slope, times your adjusted gross score minus the Course Rating, with a small playing-conditions adjustment when the field scored unusually high or low. A 90 on that slope 125, rating 71.5 course is a differential of about 16.7. The World Handicap System asks for at least 54 holes before it issues a first Index, and it updates after every round you post. Enter a score here and the tool returns that round's differential.
What this leaves out
This computes a Course Handicap and a single round's differential, the two pieces of arithmetic a golfer actually needs at the first tee. It does not track your 20-round record or compute the full Index, which needs your posting history, and it does not apply the handicap allowance that competitions layer on top, such as 95% for individual stroke play, which your event rules set. For those, your golf association's app holds the record. For working out how many strokes you get on a strange course today, the number above is the one that matters.
A quick gut check: if your Course Handicap comes out lower than your Index on a course rated below its par, the formula is working, not broken.
Frequently asked questions
How is a course handicap calculated? Course Handicap equals your Handicap Index times the Slope Rating divided by 113, plus the Course Rating minus Par. On a slope 125, rating 71.5, par 72 course, an 18.0 index gives 18 times 125 over 113, which is 19.9, plus 71.5 minus 72, which is minus 0.5, for a Course Handicap of 19. The 113 is the standard slope, so a harder course above 113 raises the number.
What is the difference between a Handicap Index and a Course Handicap? A Handicap Index is your portable measure of ability, one number that travels to any course. A Course Handicap converts it to the strokes you get on a specific set of tees, using that tee slope and rating. You carry one Index and compute a fresh Course Handicap at each course, which is why the same golfer plays off a different number on an easy course than on a hard one.
How is the Handicap Index itself worked out? Your Handicap Index is the average of the best 8 Score Differentials from your most recent 20 rounds, rounded to one decimal. Each round produces a Score Differential of 113 divided by the Slope, times your adjusted gross score minus the Course Rating. The World Handicap System recommends at least 54 holes before it issues a first Index. This tool computes a Score Differential for one round when you enter a score.
Why do some calculators give a different course handicap? Because many older tools still use the pre-2020 formula, Handicap Index times Slope over 113, and drop the Course Rating minus Par term the World Handicap System added in 2020. On a course rated well above or below its par, that term shifts the answer by several strokes. A course rated 75 at par 72 adds three strokes that the old formula misses, so this tool shows that adjustment separately.
What is a Playing Handicap? A Playing Handicap is the Course Handicap after a handicap allowance for the format, such as 95% in an individual stroke-play competition or other percentages in fourballs and team events. The allowance keeps different formats fair. This tool reports the Course Handicap, which is the starting point, and your competition rules set the allowance applied on top of it.