Calculate your golf handicap index.

Work out each score differential

Your differential tells you how well you played against the difficulty of the course: (113 ÷ slope) × (adjusted gross score − course rating). Shoot 88 on a course rated 71.2 with a slope of 128 and your differential is 113 ÷ 128 × 16.8 = 14.8. A slope of 113 marks a course of standard difficulty, so a harder course shrinks your differential and an easier one stretches it.

Count your lowest differentials

With 20 rounds or more, your index is the average of your best 8 of your most recent 20 differentials. With fewer rounds, fewer count, and the shortest records take an adjustment: your lowest one minus 2.0 with 3 rounds, minus 1.0 with 4. Open the table under the calculator to see the row that applies to you; the rounds that count glow green.

Cap each hole at net double bogey

Before you add up your score, cap every hole at net double bogey: par plus 2 plus the strokes you get on that hole. On a par 4 where you get one stroke, the most you post is 7, even if you made 9. You keep one blow-up hole from wrecking your index, which is the point of the cap.

Know what this number leaves out

Your club's official index adds four things this calculator leaves out. The playing conditions calculation shifts the differentials of everyone who played on a day when scores ran far above or below normal. The soft cap slows your index when it climbs more than 3.0 above your lowest index of the last year, and the hard cap stops it at 5.0 above. An exceptional round, with a differential 7.0 or more below your index, takes 1.0 or 2.0 off. Read them in Rule 5 of the Rules of Handicapping.

Track your index after every round

Add your course to Scratchmaxx once, with its pars, stroke indexes, course rating and slope, then keep your card hole by hole. Each finished round caps its own holes at net double bogey and moves your index with the same table you see here. Keeping your rounds and your index costs nothing.