90 on slope 130 — differential 15.6

Same score, other courses

A bigger slope divides 113 by more, so the differential comes out smaller. Ninety strokes on a slope-155 course is a far better round than ninety on a slope-95 course. The rules allow slopes from 55 to 155, and most courses land between 105 and 145.

The formula is one multiplication

Differential = (adjusted gross score − Course Rating) × 113 ÷ Slope Rating. 113 is the slope of a course of standard difficulty, so on such a course the multiplier is exactly one and changes nothing. This table assumes a par-72 course rated 72.0, which isolates what the slope alone does.

One round is not an index

A Handicap Index is the average of the best eight differentials from your last twenty rounds. What this table gives is therefore not an index but **the differential a single round produces**. That averaging is also why one good day barely moves an index: only eight of twenty scores count, and the other twelve do nothing.

Nearby slopes

Same course, other scores

What this table assumes

It assumes a par-72 course rated exactly 72.0. Real courses rate above or below par, and that gap enters the arithmetic directly. The adjusted gross score is also capped hole by hole at net double bogey, so it can differ from what you actually wrote down, and a playing-conditions adjustment may be applied for the day.

How to read this

• Differential = (gross score − Course Rating) × 113 ÷ Slope.
• 113 is standard difficulty, so at slope 113 nothing changes.
• The higher the slope — the harder the course — the better the same score reads.
• A Handicap Index averages the best eight of your last twenty rounds.