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A handicap is a numerical measure of a golfer's potential playing ability based on the tees played for a given course. It is used to calculate a net score from the number of strokes actually played during a competition, thus allowing players of different proficiency to play against each other on somewhat equal terms. The higher the handicap of a player, the poorer the player is relative to those with lower handicaps. "Official" handicaps are administered by golf clubs or national golf associations. Exact rules relating to handicaps can vary from country to country.
Handicap systems are not used in professional golf. Amateur golfers who are not members of golf clubs are generally ineligible for "official" handicaps.
A handicap is calculated with a specific arithmetic formula that approximates how many strokes above or below par a player might be able to play, based on his ten best scores. The R&A (now a separate organization from the Royal and Ancient Golf Club), based in St Andrews, Scotland has no jurisdiction over handicapping. The administration of handicapping systems in countries affiliated to the R&A is the responsibility of the national golf associations of those countries. These bodies specify slightly different ways to perform this calculation for players. The details of these calculations are presented below.
A golfer's net score is determined by subtracting the player's handicap from the gross score (the number of strokes actually taken). The net scores of all the competing golfers are compared and (generally) the person with the lowest score wins.
Contrary to popular opinion, a player's handicap is intended to show a player's potential, not a player's average score. The frequency by which a player will play to their handicap is a function of that golfer's handicap, as low handicappers are statistically more consistent than higher handicappers. The USGA refers to this as the "average best" method. So in a large, handicapped competition, the golfer who shoots the best with respect to his abilities and the normal variations of the score should win.
While there are many variations in detail, handicap systems are generally based on calculating an individual player's playing ability from his recent history of rounds. Therefore, a handicap is not fixed but is regularly adjusted to increases or decreases in a player's scoring.
In the United States, handicaps are calculated using several variables: The player's scores from his most recent rounds, and the course rating and slope from those rounds. A "handicap differential" is calculated from the scores, using the course slope and rating, and the player's handicap differentials are used to calculate the player's handicap.
Scratch and bogey golfers 
A golfer whose handicap is zero is called a "scratch golfer." A golfer whose handicap is approximately 18 is called a "bogey golfer."  It is possible to have a handicap below 0; these are referred to as 'plus' handicaps, and at the end of the round, a 'plus' handicap golfer must add his handicap to his score. If his handicap is a plus number, like +3, then adding that number to the number of total strokes will actually increase that golfer's final score. If a player shoots a 69 and has a plus 3 handicap, his final score will be 72.
Course rating and slope 
In the United States each officially rated golf course is described by two numbers, the course rating and the slope rating. The course rating of a particular course is a number generally between 67 and 77 that is used to measure the average "good score" by a scratch golfer on that course. The slope rating of a particular course is a number between 55 and 155 that describes the relative difficulty of a course for a bogey golfer (defined above) compared to a scratch golfer. These two numbers are used to calculate a player's handicap differential, which is used to adjust a player's score in relation to par according to the slope and rating of the course. The slope rating for a golf course of average difficulty is 113.
For each officially posted round, the player's handicap differential is calculated according to the following formula:
The differential is rounded to the nearest tenth.
|Number of rounds||Differentials to use|
|5 or 6||lowest 1|
|7 or 8||lowest 2|
|9 or 10||lowest 3|
|11 or 12||lowest 4|
|13 or 14||lowest 5|
|15 or 16||lowest 6|
The handicap index is then calculated using the average of the best 10 differentials of the player's past 20 total rounds, multiplied by 0.96. Any digits in the handicap index after the tenths are truncated. If a golfer has at least 5 but fewer than 20 rounds posted, the index is calculated using from one to nine differentials according to the following schedule:
Updates to a golfer's index are calculated periodically according to schedules provided by state and regional golf associations.
The handicap index is used with the course's slope rating to determine the golfer's course handicap according to the following formula:
The course rating is not used to determine a course handicap. The result is rounded to the nearest whole number.
The course handicap is the number of strokes to be deducted from the golfer's gross score to determine the net score.
For example, the following table shows the impact of the same score at two different tee positions at the same course, and the resulting handicap differential:
- Gross score: 85
- Course rating: 69.3
- Course slope: 117
- Yields a handicap differential of 15.2. If this golfer's handicap index is 10.5, the course handicap would be and the net score would be 85 − 11 = 74.
- Gross score: 85
- Course rating: 71.9
- Course slope: 124
- Yields a handicap differential of 11.9. If this golfer's handicap index is 10.5, the course handicap would be and the net score would be 85 − 12 = 73.
Additionally, before making the above calculation, the gross score must be adjusted using the equitable score control table, which removes the effect of abnormally high individual hole scores by establishing a maximum score per hole depending on the player's handicap index. For example, a golfer with a course handicap of 20 through 29 can record a maximum of 8 strokes on any one hole for handicap calculation purposes only.
Calculating a score 
The handicap is used to determine on which holes a player (or team) is granted extra strokes. These are then used to calculate a "net" score from the number of strokes actually played ("gross" score).
To find how many strokes a player is given, the procedures differ between match play and stroke play. In match play, the difference between the players' (or teams') handicaps is distributed among the holes to be played. For example, if 18 holes are played, player A's handicap is 24, and player B's handicap is 14, then A is granted ten strokes: one on each of the ten holes identified by the handicap numbers 1 through 10 on the scorecard and no strokes on the remaining eight. If A's handicap is 36 and B's handicap is 14, A is granted 22 strokes: one on each of the 18 holes to be played, and an additional one on each of the four holes identified by the handicap numbers 1 through 4 on the scorecard.
The procedure in stroke play is similar, but each player's individual handicap (rather than the difference between two players' handicaps) is used to calculate extra strokes. Therefore, a player with handicap 10 is granted one stroke on each of the ten holes identified by the handicap numbers 1 through 10 on the scorecard and no extra strokes on the remaining eight. A player with a handicap of 22 is granted 22 strokes: one on each of the 18 holes and an additional one on each of the four holes identified by the handicap numbers 1 through 4 on the scorecard.
Example for the calculation of "net" results: Assume that A is granted one stroke on a par four hole and player B is granted none. If A plays six strokes and B plays five, their "net" scores are equal. Therefore, in match play the hole is halved; in stroke play both have played a "net" bogey (one over par). If both play five strokes, A has played better by one "net" stroke. Therefore, in match play A wins the hole; in stroke play A has played a "net" par and B a "net" bogey.
Specific example 
Let's say that we have four golfers: Andy, Bob, Chris, and Dan, of various abilities who are in a competition against each other. To the right are the players and their handicap indices. The course (from the tees being played) has the following slope: 120.
|Andy||(120/113) * 14.8||15.72||16|
|Bob||(120/113) * 9.9||10.51||11|
|Chris||(120/113) * 1.5||1.59||2|
|Dan||(120/113) * 26.4||28.04||28|
So, using the formulas above, here are their course handicaps from the tees being played (note that only the slope is used to determine the handicap):
|Andy||91||91 - 16 = 75|
|Bob||86||86 - 11 = 75|
|Chris||74||74 - 2 = 72|
|Dan||99||99 - 28 = 71|
And, finally, to the right are their gross and their net scores. Dan wins because he is the only one in the group who actually shot better than his handicap.
Slope rating 
The slope rating is the USGA mark that indicates the measurement of the relative difficulty for a bogey golfer compared to the course rating. Slope rating is computed from the difference between the bogey rating and the course rating. The lowest slope rating is 55 and the highest is 155. The average slope rating is 113. To compute the handicap strokes from a given set of tees on a specific course with a slope of "s" given a handicap index of "h," the following formula is used: (s/113)*h rounded to the nearest integer.
Example: A male golfer plays a course with Slope Rating 126, and Course Rating 72.5. Per the formula, compute 126 / 5.381 + 72.5 = 95.9 - which predicts the bogey golfer's average of his ten best (out of twenty) scores would be approximately 95.9 from this particular set of tees.
History of the USGA system 
The USGA has often resorted to the courts to protect the integrity of its handicap system. In one such case, the California Court of Appeal (First District) summarized the system's history:
|“||The USGA was founded in 1894. One of its chief contributions to the game of golf in the United States has been its development and maintenance since 1911 of the USGA handicap system . . . designed to enable individual golf players of different abilities to compete fairly with one another. Because permitting individual golfers to issue their own handicaps to themselves would inevitably lead to inequities and abuse, the peer review provided by authorized golf clubs and associations has always been an essential part of the [system]. Therefore, in order to protect the integrity and credibility of its [handicap system], the USGA has consistently followed a policy of only permitting authorized golf associations and clubs to issue USGA handicaps . . . . In 1979, USGA assembled a handicap research team to investigate widespread criticisms of USGA's then-existing handicap formula. The research team invested approximately a decade and up to $2 million conducting intensive analysis and evaluation of the various factors involved in developing a more accurate and satisfactory [system]. As a result, the research team developed new handicap formulas . . . designed to measure the overall difficulty of golf courses, compare individual golfers with other golfers of all abilities, take account of differences between tournament and casual play, and adjust aberrant scores on individual holes. USGA subsequently adopted and implemented these new [f]ormulas between 1987 and 1993.||”|
Handicapping in the United Kingdom and Ireland 
In the UK and Republic of Ireland, a "scratch score" system was previously in place in order to rate courses and be fair to golfers of varying ability, and to make allowances that courses may play "easier" or "harder" than par, overall, to the amateur field. For this reason, a "standard scratch score" (SSS) is used as a baseline for how the course plays in practice (e.g. an SSS lower than par indicates a course which golfers find slightly easier, and vice versa).
Akin to the SSS is the Competition Scratch Score (CSS). The principle is the same, only this describes how easy or difficult the course played during a given competition. It is against this CSS score that a player's handicap is adjusted by the club. Golfers with a handicap of 5 or lower are said to be Category 1 players. Higher handicap players are categorised as Category 2, 3, or 4. For every stroke the Category 1 golfer's net score is below the CSS, his handicap is reduced by 0.1. For Category 2 golfers, this figure is 0.2, for Category 3 golfers it is a 0.3 reduction, and 0.4 for Category 4 golfers.
Similarly, amateur golfers are allowed a buffer zone to protect their handicap on "off-days". For Cat 1 this is 1 stroke, for Cat 2 this is 2 strokes, etc. This means that if a Category 1 golfer's net score is one stroke higher than the CSS, his handicap will not increase. If a golfer's net score is higher than the CSS plus buffer zone combined, his handicap will increase by 0.1. This 0.1 increase covers all golfers and does not vary by category.
Although they can be done manually, computer software now must be used to calculate the CSS and in Ireland and England handicaps are now published to a Centralised Database of Handicaps (CDH). CDHs are also being introduced in Scotland and Wales in 2011.
EGA Handicap System 
The “EGA Handicap System” is the EGA’s (European Golf Association) method of evaluating golf abilities so that players of different standards can compete in handicap events on equal terms.
An “EGA Playing Handicap” is the number of Handicap Strokes a player receives for a specific set of Tees at the course being played. The Playing Handicap is expressed as a whole number (0.5 is rounded upwards, -0,5 (“plus” 0.5) rounds upwards to 0 (scratch) and -1.5 (“plus” 1.5) to -1 (“plus” 1).
Note 1: If a player’s Playing Handicap is negative (a so-called “Plus” Playing Handicap) he gives Handicap Strokes to the course, commencing at stroke index 18.
Note 2: The Playing Handicap is considered to be the “Handicap” referred to in Rule 6-2 of the Rules of Golf.
The “EGA Playing Handicap Formula” converts EGA Exact Handicaps into EGA Playing Handicaps: Playing Handicap = Exact Handicap x (Slope Rating / 113) + (Course Rating - Par)
Under the EGA system, final scores might be amended using the Competition Stableford Adjustment method.
Australian Handicap System 
Australian Golf handicaps are maintained by GOLFLink which was a world-first computerised handicapping system developed by Golf Australia’s predecessor, the Australian Golf Union in the 1990s. The AGU operated from 1898 until it merged with Womens Golf to form GA in 2006. Together with its State/Territory bodies, GA represents 445,000 amateur golfers belonging to 1530 Golf Clubs, and sits alongside bodies representing the Pros, Superintendents, Managers and Architects. When GOLFLink was first introduced it contained two key characteristics that set it apart from other world handicapping systems:
1. It relied on a Calculated Course Rating to determine how difficult the course was on the day, and upon which handicap adjustment was made
2. It utilised a 'swipe' card that enabled a player to access his handicap from any GOLFLink terminal in Australia
In April 2010 GA adopted the USGA calculation method using the average of the best 10 differentials of the player's past 20 total rounds, multiplied by 0.96. In September 2011 this was altered to the best 8 out of 20 rounds, multiplied by 0.93. In addition an ‘anchor’ was introduced so that no player is permitted to increase his handicap by more than 4 in a rolling 12 month period. The reasons for these changes were cited to restore equity between high and low markers. Rather than introduce the USGA Slope system, GA intends to introduce a more sophisticated version of CCR – The Daily Scratch Rating (by Mar 2013)
- "USGA Handicap System Manual – usga.org – Retrieved June 18, 2011". usga.com. Retrieved June 18, 2011.
- United States Golf Ass'n v. Arroyo Software Corp., 69 Cal. App. 4th 607 (1999).
- USGA Handicap System (used in the United States and Mexico)
- Unified Handicapping System by the Council of National Golf Unions (used in Great Britain and Ireland)
- Australian Handicap System
- South African Golf Association Handicap System (used in South Africa)
- Golf handicap FAQ (US Rules)
- EGA Handicap System (used in continental Europe)