What a score differential means

A score differential is one round, translated so it can be compared with rounds on other courses. A 90 at a short course and a 90 at a championship course are not the same golf. The differential says how far the adjusted score sat above the course rating, then scales that gap by 113 ÷ slope.

The formula for 18 holes is (113 ÷ slope) × (adjusted gross score − course rating − PCC). The result is rounded to the nearest tenth. A negative differential means you beat the rating. That is allowed, and it helps an index.

Adjusted, not gross

The score in the formula is the adjusted gross score. Any hole worse than net double bogey is cut back to that number before you add the card up. Net double bogey is par + 2 + the strokes your course handicap gives you on that hole. A blow-up 9 on a par 4 does not keep its full weight.

The day itself

PCC, the playing conditions calculation, moves the differential by a whole number from −1 to +3 when the whole course played unusually hard or easy. A calculator on a website cannot see every score posted that day, so it cannot produce the PCC. If your association published one, type it. Otherwise it stays 0, and the page says so.

Differentials, not raw scores, are what the index averages. The score differential calculator does one round. The handicap calculator does the record.