This is how the USGA defines a handicap differential:
A "Handicap Differential" is the difference between a player's adjusted gross score and the USGA Course Rating of the course on which the score was made, multiplied by 113, then divided by the Slope Rating from the tees played and rounded to the nearest tenth, e.g., 12.8.
If you look at this statement in more of a mathematical formula, it looks like this:
Handicap Differential = (Adjusted Gross Score - Course Rating) x 113 ÷ Slope Rating [result rounded to nearest tenth]
The number 113 is considered the normative or standard slope for a course. To see how this formula fits into the overall calculation of a USGA Index and Course Handicap, please see our plain English explanation.
Our Handicap Systems use the exact USGA formulas including the one for calculating the handicap differentials.