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Golf Handicaps Decoded

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9 versus 18 Hole Handicaps

When golfers first sign up with MyScorecard they are given the choice of a 9-hole or an 18-hole handicap. For those who sometimes play nine and sometimes play eighteen, this can be a confusing decision. In this article, we hope to shed some light on the difference between the two handicaps and which may be right for you.

Before we dive in, you should have a basic understanding of how your handicap is calculated. At the fundamental level we take your score and adjust it for the course difficulty by subtracting the course rating and then dividing the result by the course slope. The resulting number is called the 'differential' and the formula for reference is (score - rating) * (113 / slope). (Please note that we have left out some very important steps that are not relevant for this discussion - we would encourage you to visit the article explaning the Handicap Formula, also found in this section of the Knowledge Center.)

When we talk to MyScorecard members about 9-hole handicaps, the same four questions tend to be asked:
  • What is a 9-hole handicap?
  • What adjustment do I need to make to track a 9-hole handicap?
  • Can I enter both 9 and 18-hole scores into my Scorecard?
  • So which type of handicap should I use (or does it really matter)?
What is a 9-hole handicap?

In this busy day and age, many golfers don't have time to get in a full 18 holes every time they play. In fact, quite a few only play 9 holes at a time. Instead of forcing these golfers to combine their scores every time they play, the USGA created a 9-hole handicap, which is denoted by an "N" (as in 12.2N). Golfers who have 9-hole handicaps can compete as normal against other 9-hole handicap players by giving the difference between their handicaps over the nine holes (a 9N gives a 12N three strokes on a course with a 113 slope - but only on nine holes. If they play eighteen, the 12N receives 6 strokes ). When a 9-hole handicap golfer plays against an 18-hole handicap golfer, they simply double their handicap (12N becomes a 24) and are able to compete fairly.

What adjustments do I need to make to track a 9-hole handicap?

It turns out that the exact same formula is used to calculate both 9-hole and 18-hole handicaps. The only thing that changes is the rating number. Nine-hole handicappers need to use the 9-hole rating or halve the 18-hole rating when entering their scores. From a quick look at the handicap calculation, you can see how entering an 18-hole rating (70.1) when tracking a 9-hole score (46) results in a negative differential and ruins the handicap calculation.

(46 - 70.1) * (113 / 121) = -23

The rating traditionally denotes what the "Scratch" golfer would shoot on eighteen holes. We halve the number and that allows an approximation of what the "Scratch" golfer would shoot on nine holes. The slope number doesn't change because that denotes how much harder the course is for a "Bogey" golfer rather than for a "Scratch" golfer. If the course is twice as hard for eighteen holes, it still stays twice as hard for nine holes (more information on the slope and the rating can be found in the article discussing the slope and rating in this section).

So it would seem that if a golfer entered the correct rating numbers, they could enter both 9-hole and 18-hole rounds into their scorecard. Well, not exactly. Let's take the example below where a golfer plays two rounds, the first on eighteen holes and the second on nine. We'll calculate the differential for each:

(46 - 35.1) * (113 / 121) = 10.2
(92 - 70.2) * (113 / 121) = 20.4

The next step in the handicap calculation is to take the best ten differentials from the last twenty scores. But wait - our golfer would have to have a pretty amazing round for any 18-hole differential to actually be lower than a 9-hole differential. For those who evenly mix 9-hole scores and 18-hole scores on their Scorecard, there's over a 99% chance that all the stars will appear next to the 9-hole scores. In fact, the handicap calculation will almost always choose 9-hole scores over 18-hole scores - even if they are much worse games - thus skewing your handicap.

Avoiding this skew is the reason you should only enter in 9-hole scores, or 18-hole scores - but not both.

So which type of handicap should I use (or does it really matter)?

If you shoot half your score on nine-holes (46 versus 92) and then divide the rating in half (35.1 versus 70.2), does it really matter whether you use a 9-hole or an 18-hole handicap? Are they not essentially interchangeable?

Well, again not exactly. The above assumption rests on the fact that every time you play eighteen holes you'll have the same score on both nines. But that isn't true - we're not yet sure as to whether you end up with a better or worse handicap (any thoughts from the statistically inclined are most welcome), but it will be slightly different.

As an example, we borrowed the scores from one of our members. As you can see, the distribution of their differentials when looking on a 9-hole basis is much wider than when looking on an 18-hole basis.

9 and 18-hole differentials

But a much more important reason goes back to the original intent of the handicap formula, which was to provide an even basis of competition for all golfers. Much like computer operating systems, such a standard only really works when used by a majority of the people. To use a different handicap formula defeats the purpose of the handicap system. While the differences between 9 and 18-hole handicapping schemes may be minimal, when in doubt you should choose the handicap method that most people use - the 18-hole handicapping method. Only when an 18-hole handicap is truly an inconvenience should you choose to use a 9-hole handicap.

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