We use the USGA Method formula to calculate the index. When we have more than 20 scores in the system, we calculate the index based on the best 10 of the last 20. For 5-20 scores we use a standard table to determine how many scores to use and return the current handicap. For less than 5 score, USGA Method does not compute a handicap. In Handicap Server you have the option to get a handicap even for 4 scores by either taking the best score or the average.
European Golf Association
The official method devised by the European Golf Association and used
in the 40 European Federations. The method relies on Stableford Points
and Handicap Categories to update the handicap.
More details about the EGA method can be found here:
EGA® Handicap Manual
This method is very popular due to its simplicity. After each round of
golf, we look at the most recent X scores, we throw away the worst Y
scores and we average the rest. Popular combinations of X and
Y are X = 3 & Y = 0 or X = 5 & Y = 2. This method provides a handicap
immediately after the first score, by ignoring scores that need to be
Weighted Averages (Exponential Smoothing)
The Exponential Smoothing method in Mathematics is a technique applied
to time series data (such as golf scores) in order to make forecasts.
Your first handicap is the differential that is linked to the first
score that you post. After each score posting we refine the handicap
using a weighted average (you can choose the weight) between the
previous handicap and the new differential.
Average All Differentials
Based on the proposal of our clients we developed 'All Average Differential' which is a pretty simple method that computes the average of differentials if less than four scores introduced. If there are between five and twenty scores, we throw away the worst and the best differential then compute the averaged of those which remained. If there are more than twenty scores, we take last twenty and calculate the average as in the cases above.
Edward Gobran's Method
'Edward Gobran's Method' starts with an initial handicap for all players. When the
first score is registered, the new handicap is 1/4 of the score plus 3/4 of the initial
handicap. The result is multiplies by 0.96, similar to the USGA Method. The second score and beyond modifies the handicap as follows: 0.2 of the initial handicap
plus 0.4 of the first score plus 0.4 of the second score. A 96% percentage is applied to the final result.