How this calculator works
This calculator produces a Handicap Index using the World Handicap System (WHS), the system jointly maintained by the USGA and The R&A and used by golf associations worldwide since 2020. Enter score differentials directly if you already have them, or switch to raw mode and enter the adjusted gross score, course rating and slope rating for each round — the calculator computes the differentials for you using the official formula.
The Handicap Index is not simply an average of all your rounds. It only counts your best rounds, on the idea that a handicap should represent your demonstrated potential rather than your typical score. With 20 or more rounds on file, it is the average of the 8 lowest differentials from your most recent 20 scores. With fewer than 20 rounds, an official table (reproduced below) sets both how many of your lowest differentials to average and a fixed point adjustment, since averaging just 1 or 2 good rounds would otherwise understate a new golfer's true handicap.
The formulas
Score Differential = (Adjusted Gross Score − Course Rating) × 113 ÷ Slope RatingHandicap Index = average of the lowest N differentials (from the counts table below) + adjustment, rounded to 1 decimal113 is the slope rating of a course of 'standard' difficulty, so it normalizes every course to a common baseline. This calculator does not apply the WHS Playing Conditions Calculation (PCC), a small day-to-day adjustment some regions apply for unusual weather — most golfers' handicaps are close enough without it.
Worked example: 4 rounds, differentials 16.3, 14.8, 18.4, 20.7
- With only 4 score differentials on file, the WHS counts table (Rule 5.2a) says: use the lowest 1, with a −1.0 adjustment.
- The lowest of the 4 differentials is 14.8.
- Handicap Index = 14.8 + (−1.0) = 13.8.
- Once this golfer has posted 20 rounds, the calculation switches to averaging the lowest 8 of the most recent 20, with no adjustment.
Frequently asked questions
Why does the calculator sometimes subtract points even though my rounds don't change?
The WHS counts table applies a fixed negative adjustment for very small sample sizes (3, 4, or 6 scores) because averaging just your single best round out of only 3-4 rounds tends to understate how good you really are. The adjustment corrects for that until you have enough rounds for the average itself to be reliable.
What counts as an 'adjusted gross score'?
It is your actual score after applying WHS net double bogey caps to any exceptionally high holes — the maximum score you can post on any hole is capped at net double bogey. This calculator assumes you enter that already-adjusted score, not your raw, uncapped scorecard total.
Why does a higher slope rating lower my differential for the same score?
Slope rating measures how much harder a course plays for a bogey golfer relative to a scratch golfer — a higher slope means the course is comparatively tougher. Dividing by a larger slope reduces the differential, which credits you for shooting the same score on a harder course.
Do I need exactly 20 rounds, or does it work with fewer?
It works with as few as 3 rounds, the WHS minimum for establishing a Handicap Index. Between 3 and 19 rounds, the official counts table changes both how many of your lowest differentials are averaged and whether an adjustment applies; at 20 or more, it's always the lowest 8 of your most recent 20 rounds with no adjustment.
Is this the same Handicap Index my golf club or app shows me?
It uses the same official formulas, but your club's number may differ slightly if it applies the optional Playing Conditions Calculation, uses exact WHS-certified course and slope ratings, or includes rounds this calculator does not have. Treat this as a close, formula-accurate estimate rather than your official record.