You calculate your golf handicap index from score differentials, one number per round that compares your adjusted score with the course rating and slope of your tees. Once you have 20 rounds, you average your best 8 differentials from your last 20, round to the nearest tenth, and that number is your handicap index.
You can start sooner. From your third round, a short table tells you how many differentials to average and what to subtract, and your index tops out at 54.0. Work through the steps below in order, then follow one round from the card all the way to your next course handicap.
Turn each round into a score differential
Rule 5.1a of the Rules of Handicapping gives the formula for an 18-hole round:
Score differential = (113 ÷ slope rating) × (adjusted gross score minus course rating minus PCC)
Here's what each piece means for you:
- Adjusted gross score: your total after you cap every hole at net double bogey (next section).
- Course rating: the score you'd expect from a scratch golfer on your tees, in strokes to one decimal, such as 70.9.
- Slope rating: how much harder your tees play for a bogey golfer than for a scratch golfer. A course of standard difficulty carries a slope of 113, so on that course the first bracket equals 1.
- PCC: the playing conditions calculation, from minus 1.0 to plus 3.0, which adjusts for days when the course played harder or easier than normal. On your own, you set it to 0.
Round the result to the nearest tenth, with .5 going up. Post an adjusted 95 from tees with a course rating of 72.1 and a slope of 131, and you get (113 ÷ 131) × 22.9 = 19.75, so you record 19.8.
Cap every hole at net double bogey
Before you add up your score, cap each hole. Net double bogey equals par, plus 2, plus any handicap strokes you receive on that hole (The R&A, Rule 3). Your course handicap tells you how many strokes you get, and the stroke index on the card tells you where they fall:
- With a course handicap of 14, you get one stroke on the holes with stroke index 1 to 14.
- With a course handicap of 21, you get one stroke on every hole and a second on stroke index 1, 2 and 3.
So at 21, a par 4 with stroke index 12 caps at 7, and a par 5 with stroke index 1 caps at 9. Make a 10 on that par 4 and you write 7 for handicap purposes. You can apply the cap on as many holes as you need in one round. Until you hold an index, every hole caps at par plus 5 instead.
Count the differentials your record allows
With 20 or more rounds, you average the lowest 8 of your most recent 20 differentials. With 3 to 19, you follow this table from the USGA's Rule 5.2a:
| Differentials in your record | Differentials you use | Adjustment |
|---|---|---|
| 3 | Lowest 1 | minus 2.0 |
| 4 | Lowest 1 | minus 1.0 |
| 5 | Lowest 1 | 0 |
| 6 | Average of lowest 2 | minus 1.0 |
| 7 or 8 | Average of lowest 2 | 0 |
| 9 to 11 | Average of lowest 3 | 0 |
| 12 to 14 | Average of lowest 4 | 0 |
| 15 or 16 | Average of lowest 5 | 0 |
| 17 or 18 | Average of lowest 6 | 0 |
| 19 | Average of lowest 7 | 0 |
| 20 | Average of lowest 8 | 0 |
You need scores from at least 54 holes for your first index. Say your first three differentials come out at 24.6, 27.1 and 22.9. You take the lowest, 22.9, subtract 2.0 and start at 20.9. You round every result to the nearest tenth, and your index never climbs past 54.0, the maximum under Rule 5.3. Check your own numbers in the handicap calculator.
Convert your index into a course handicap
Your index describes how you play on a course of standard difficulty. Before each round, convert it for the tees you play (USGA, Rule 6.1a):
Course handicap = index × (slope rating ÷ 113) + (course rating minus par)
Round to the nearest whole number, .5 going up. Take an index of 12.4 to tees with a slope of 135, a course rating of 73.0 and a par of 72: 12.4 × 1.1947 + 1.0 = 15.81, so you get 16 strokes. On easier tees, where the course rating sits below par, the second bracket turns negative and takes strokes away. Run any set of tees through the course handicap calculator before you tee off.
Work one full example from card to index
Here's a made-up round with real arithmetic. You carry a 19.9 index from 7 differentials: 21.4, 19.5, 25.1, 22.8, 24.0, 20.3 and 23.5. With 7 rounds, you average your lowest 2: (19.5 + 20.3) ÷ 2 = 19.9.
You play the white tees: par 72, course rating 70.9, slope 127.
- Course handicap. 19.9 × (127 ÷ 113) = 22.37. Add 70.9 minus 72, which is minus 1.1, and you reach 21.27. You round to 21.
- Strokes. At 21, you get one stroke on every hole and a second on stroke index 1, 2 and 3.
- Net double bogey. You shoot 93. On hole 6, a par 4 with stroke index 12, you make 9. Your cap there is 4 + 2 + 1 = 7, so you write 7. On hole 3, a par 5 with stroke index 1, you make 9. Your cap there is 5 + 2 + 2 = 9, so the 9 stands. Every other hole sits under its cap, so your adjusted gross score is 91.
- Differential. (113 ÷ 127) × (91 minus 70.9) = 0.8898 × 20.1 = 17.88. With PCC at 0, you round to 17.9.
- New index. You now hold 8 differentials, and your lowest two are 17.9 and 19.5. Their average, 18.7, becomes your index.
- Next course handicap. On the same tees, 18.7 × (127 ÷ 113) minus 1.1 = 19.92, so you get 20 strokes next time instead of 21.
One good round dropped your index by 1.2, because it pushed 20.3 out of the two differentials that count.
Know what the official system adds
Your own math covers the core of the World Handicap System. An official Handicap Index adds safeguards from The R&A's Rule 5 and a few steps you can't run alone:
- Soft cap. Once you have 20 scores, your record tracks a Low Handicap Index, the lowest index you held over the previous 365 days. When a new index lands more than 3.0 above that low, you keep only half of the rise past 3.0. From a low of 12.0, a new 16.0 becomes 15.5.
- Hard cap. After the soft cap, your index can't rise more than 5.0 above your low.
- Exceptional score reduction. Post a differential 7.0 to 9.9 below your index and your index drops a further 1.0. At 10.0 or more below, it drops 2.0.
- Playing conditions calculation. Each day, PCC compares the scores golfers post at your course with expected scoring. It needs at least 8 acceptable scores from players with an index of 36.0 or below, and it returns minus 1.0, 0, plus 1.0, plus 2.0 or plus 3.0. You can't see everyone's scores, so you leave it at 0.
- Nine-hole rounds. Post 9 holes and the official calculation pairs your 9-hole differential with your expected score for the other 9.
- Posting and review. An official index needs membership in a golf club affiliated with an authorized association. In the US, you post through the USGA's GHIN, your index updates by the day after you post, and a handicap committee can review it.
Keep your own index between official posts
In Scratchmaxx, you enter your course one time, with the pars, the stroke indexes, and the course rating and slope of the tees you play. Then you fill in the round card hole by hole with strokes, putts, fairways, greens and bunkers. Your index runs on the core math of the World Handicap System: your best 8 differentials from your last 20 rounds, a net double bogey cap on every hole, the short-record table from 3 to 19 rounds, and a ceiling of 54.0.
That number leaves out the soft cap, the hard cap and the exceptional score reduction, so expect it to drift from an official index after a slump or a career round. Use it to follow your own progress. For an official Handicap Index, you go through a golf club or association, and in the US that means GHIN.
Your rounds, your card, your stats and your index cost nothing. Mark each shot and the club you hit, and the same rounds give you your average score, fairways hit, greens in regulation, putts per round, score by par, and the median carry of every club to set against the golf club distance chart.
