Enter your 9-hole score, the 9-hole course rating and slope, and your Handicap Index. You'll see the 18-hole score differential that goes on your record, worked out the way the World Handicap System has done it since 2024.
Calculator
The 9-hole course rating and slope are on the course's rating card, for the front and back nine. Use a + for a plus handicap, such as +1.2.
Use your adjusted gross score for the nine, with each hole capped at net double bogey. Your official differential can also include the day's playing conditions calculation, which this calculator leaves out.
The expected 9-hole differential depends only on your Handicap Index. The rules don't publish its formula. This calculator uses 0.52 × Handicap Index + 1.2, a widely used approximation that golfers reverse-engineered from handicap calculators. It gives the USGA's published example exactly: a golfer with an index of 14.0 is expected to make 8.5 over nine holes, so a 9-hole differential of 7.2 goes on the record as 15.7. Treat the result as a close estimate, not your official figure.
Yes, if you play all nine holes from tees with a 9-hole course rating and slope. Since 2024 each 9-hole score becomes an 18-hole score differential on its own, instead of waiting to be paired with another nine.
What is expected score?
It's the differential a golfer of your Handicap Index is expected to make over nine holes on a course of standard difficulty. The system adds it for the nine you didn't play. It depends only on your index on the day.
Why is my 18-hole differential higher than double my nine?
Because only half of it is your own play. If you beat your expected nine, the other half is filled in at your expected standard, not at the standard of your good nine. A great nine still helps, just less than a great 18 would.
What if I don't have a Handicap Index yet?
Then there's no expected score to add. Your 9-hole scores count towards the 54 holes you need for a first index, and they're converted once you have one.
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