Handicap Hub: Icky Math, or How Does USGA Course & Slope Rating Affect My Handicap Index? | Oregon Golf Association

Handicap Hub: Icky Math, or How Does USGA Course & Slope Rating Affect My Handicap Index?

By Kelly Neely, Sr. Director, Handicapping & Course Rating
Click Here for Handicap Hub Archives

If you’re a curious person – which I assume most golfers are, since this game is nothing if not complex – you’re going to want to know how your handicap is calculated. Notice I didn’t say that you’re going to want to calculate it yourself. Thankfully those days are long past, and we’ve got clever, modern processes to take care of the number crunching. But if you’re a nuts and bolts golfer and like details, it helps to know the method behind the madness of a USGA Handicap Index. Besides, you can use this valuable information to impress your golfing buddies. Or irritate them. Whichever you prefer.

First, it’s highly constructive to stop fixating on your score alone. This is emotionally hard to do, but it’s healthier anyway to ditch feelings in favor of facts when dealing with handicaps. To fully understand your Index, you have to look beyond your score to see the impact of an amazing mechanism at work called USGA Course and Slope Rating.

Now for some icky math. Stay with me!

Using Equitable Stroke Control, or ESC (the maximum score you can take on a hole for posting purposes, depending on your Course Handicap), the system uses the player’s adjusted gross score and subtracts the Course Rating. That number is multiplied by 113 (the mathematical constant within the formula that represents a course of standard difficulty), and divided by the Slope Rating of the tees played (rounded to the nearest 10th). Of course, this math is automatically done for you by GHIN, but the important thing is that it produces a number referred to as a Handicap Differential.

Here’s the Handicap Differential formula again:
(Adjusted Gross score – Course Rating) x 113 / Slope Rating

A players’ Index is based on the best (lowest) Handicap Differentials in their record at the time of the revision update. For example, if a player had 20 scores in his file, the best 10 Handicap Differentials (i.e., better half) would be used to calculate their USGA / OGA Handicap Index. These 10 Differentials would be totaled and divided by the number of Differentials used, multiplied by .96 and rounded to the nearest tenth.

Once you know the significance of a Handicap Differential, it can go a long way in helping you see how your performance on a particular set of tees affects your Index. Because you now have this extra information, you will find yourself reviewing and comparing the Differentials – the “DIFF” column in your scoring record – and not be as obsessed with your score (this is my dream, anyway). It’s crucial to get this concept, because the system uses the lowest Differentials to calculate the Index; it will not always use your lowest score!

It’s important to remember that the Course Rating affect’s the player’s Index much more than the Slope Rating number. Often, golfers focus too much on what the Slope number is when it is the Course Rating number that drives the system (and the worst thing you can do is compare Slope Ratings from course to course – but that’s the subject of another article!).

Here’s what I mean:

Course A – lower Rating, higher Slope
Player shoots 85
Handicap Differential = 14.2 [(85 – 69.3) x 113/125]

Course B – higher Rating, lower Slope
Player shoots 85
Handicap Differential = 13.4 [(85 – 71.1) x 113/117]

In this example, the same score of 85 produced two disparate Differentials, and the one with the higher Rating – representing longer yardage – is the lower of the two, and likely chosen in the Index calculation. This is because yardage – what the Course Rating number is largely based upon – is a significant challenge for nearly all golfers to overcome. The 85 on Course B represents the better performance for this player.

Some players feel that if their favorite set of tees Slope number is “too high”, they will not be competitive when visiting another club. This is not necessarily true! The above example shows the significance that the Course Rating has on a player’s Handicap Differential compared to the Slope number.

If you read through to the bottom of this article, thank you. Now you have to admit the 8th grade icky math was worth it, right?

First Tee of Greater Portland
Oregon Chapter PGA
Oregon Golf Course Superintendent's Association