# Your Handicap Index — the Score Differential is the Key Number

Have you ever played with a golfer that is perplexed by their handicap index? They may say something like, “I feel like my handicap doesn’t really reflect my scores or my game.” Your first thought might be that the golfer is delusional about their game. My first thought is that they do not understand how their handicap is calculated.

So for the player that doesn’t think their handicap reflects their scores, they need to understand two things:

(1) The handicap index is about potential. That is why it is based on the most recent eight “best scores” of all the scores you post. Lou Stagner (golf stat guru) has stated in podcasts that you will only shoot your handicap 20% of the time and your scoring average will be about 3 strokes over your handicap. However, you can shoot better than your handicap too; and Stagner has tweeted “If your handicap is legit, you should beat it about once every five rounds.”

(2) Scores are not all equal. What? That’s right the difficulty of the course and the tees you play, as well as playing conditions for that day are part of the equation for an important number called a “score differential.” And it is the score differential that is used to calculate your handicap Index. In other words, two scores of 90 will not necessarily have the same differential and therefore they will affect the handicap index differently.

In general, the goal of the handicap system is to determine which scores are the best scores, considering the course difficulty and that is why course rating and slope are so important in calculating the score differential and ultimately the golfer’s handicap index.

And, yes, I am going to get geeky now and give you a formula. Below is the score differential which takes the overall rating for a course (represented by two numbers: course rating and slope), adjusted gross score, and PCC (playing condition calculation) to determine a score differential for the score posted by the player that day.

Score Differential = (113 / Slope Rating) x (Adjusted Gross Score – Course Rating – PCC adjustment)

For Example: A golfer shoots a 90 on two courses (both from the forward tees). Course “Easy” has a rating of 65.2/107 and course “Hard” has a rating of 68.6/122.

Course “Easy” differential formula = (113/107)x(90-65.2) = 26.2

Course “Hard: differential formula = (113/122)x(90-68.2) = 18.9

(if you really want to geek out – See the “Additional Information” at the end of the blog for in-depth details on adjusted gross score and playing condition calculations used in the formula.)

The golfer’s handicap is an average of the 8 lowest “score differentials” from the last 20 scores posted. The two calculations above show how shooting a 90 is not the key number that makes your handicap index move up or down. The Differentials of 26.2 or 18.9 are what will increase or decrease your handicap index.

It should be noted that a slope of 113 (in the formula) is used as a “course standard of relative difficulty.” In golf, slope is basically a mathematical representation of how difficult a course is for a bogey golfer compared to a scratch golfer.

Golfers use the overall rating to interpret the difficulty of a course. Looking at a rating of 65.2/122 we would say the course is easier for a scratch golfer than it is for a bogey golfer. Here is how to break it down…

(1) The first number (65.2) is easy to interpret because it is based on strokes and is the rating created for scratch golfers. Therefore, a course rating of 65.2 indicates the course should be easy for a scratch golfer since 65.2 is below the course par of 72. In other words, a scratch golfer has the potential to score a 65 on the course for the tees they are playing.

(2) The second number is slope and is a mathematical representation (think a line on a graph) of how difficult the course is for a bogey golfer compared to a scratch golfer. The higher the number the harder the course. And, 113 is the mathematical average used to “represent” an “average” slope rating for an “average” course which means a rating below 113 is assumed to be “easier” than the “average” course and a rating above 113 is assumed to be “harder” than the “average” course.

Now that you know the course rating/slope has such an important role in calculating a handicap index, you may be wondering (1) how is an overall course rating determined and (2) how do we know the rating truly reflects the difficulty of the course.

There is a whole process for how golf courses get their ratings and the process has 26 evaluations made for each set of tees on each hole for a course — that’s a lot of data! State golf associations oversee the golf course rating process. Most courses are reviewed or re-rated every 10 years. If during the 10-year review gap the course has made major changes, it’s the owner’s responsibility to notify the state golf association and ask for a course review.

Are overall course ratings accurate or “fair”? That’s an interesting topic for another blog post because I guarantee almost every golfer has walked away from a course saying that the course played harder (or easier) than they expected based on the rating on the scorecard.

If you choose to calculate your score differential, besides course rating/slope you will need two numbers (1) the adjusted gross score and (2) the playing condition calculation (PCC). The handicap system (GHIN) will provide the PCC. You have two options for the adjusted gross score. You can manually calculate the adjusted gross score or have the GHIN system provide the number (if you enter your score hole-by-hole). Below is more detail on each number:

(1) Adjusted Gross Score – From the USGA website, “A score for handicap purposes should not be overly influenced by one or two bad hole scores that are not reflective of a player’s demonstrated ability. In addition, incomplete scores and/or scores where a player did not hole out on every hole can provide reasonable evidence of the player’s ability and can be used for handicap purposes.”

If you enter your score in GHIN hole-by-hole the system will automatically adjust your score to the maximum hole score based on par for the hole and your course handicap for that hole; otherwise, you must do a manual calculation, using the “Net Double Bogey” formula, to reduce your score before entering your total gross score into GHIN.

Also, if you don’t complete holes but want to enter a score in GHIN you need to figure out a hole score for each hole you don’t complete or play; and what you enter depends on the status of the hole:

Scenario I. If you started a hole but did not hole out (or complete it) then you enter a “most likely score.” For that hole you take: (a) number of strokes already taken plus (b) any penalty strokes already incurred plus (c) number of strokes most likely to complete the hole.

Scenario II. If you have holes you did not play at all (say due to darkness you only played 7 of 9 holes) then you add an “adjusted score” (basically the par plus any handicap strokes for the hole).

(2) Playing Condition Calculation: The PCC is based on all the scores entered for the day for a course and if the scores are unusually high (or low) the worldwide handicap system will make an adjustment (you will see a PPC number on the impacted score on your GHIN stats page). The score differential for that round will have been calculated with the PPC number included in the formula.

The assumption is that there is a reason (e.g., weather, course setup) causing scores to be higher or lower than normal for the course that day. The PCC range is -1 to +3. A negative (-) adjustment means the course played easier than expected and a positive (+) adjustment means the course played more difficult than expected.

The GHIN system updates your handicap at midnight the day after you post (versus the old method of updating handicaps on the 15th of the month); and that is why the USGA and R&A want golfers to enter their scores on the day they play; otherwise, the GHIN software won’t reflect a PCC accurately.