How a Handicap Index is calculated
Each 18-hole score is turned into a differential with the course rating and slope rating of the tees you played. That puts a round on a hard course and a round on an easy course on the same scale. The differential is rounded to the nearest tenth.
The index is the average of your best differentials: the lowest 8 of the most recent 20. A shorter record uses fewer, from the lowest 1 of 3 up to the lowest 7 of 19, and records of 3, 4, or 6 rounds take a small adjustment. The table below has every step.
Why this is an estimate
An official index comes from your club or golf association. It also caps how fast an index can rise (the soft and hard caps), reduces it after an exceptional score, applies a daily playing conditions adjustment, and limits each hole to net double bogey. This calculator does the core averaging and assumes the scores you enter are already adjusted gross scores.
Questions
What is the difference between a Handicap Index and a Course Handicap?
The index is your portable number. A Course Handicap is the strokes you get on a particular set of tees, worked out from the index with that course's slope and rating. The course handicap calculator does that step.
How many rounds do I need?
At least three 18-hole scores. The calculation settles into its full form at 20.
What is an adjusted gross score?
Your score after capping each hole, which for most golfers is net double bogey. Your handicap app or club records it for you.
Is my data stored?
No. The math runs in your browser and nothing you type is sent anywhere or put in analytics.
Sources
Formulas and rules checked against these sources on October 28, 2026. Leagues and associations change their rules, so when your league's rulebook differs, follow your league.