If, for example, your league is based off a 200 handicap system, your handicap is worked out accordingly:
(200 - Average) x 80% = hanidcap.
For example, an average of 190:
(200 - 190) x 80% = 8
If your league is off a 210 handicap system, just replace the 200 with 210 in the formula.
It depends on who authorizes the handicap. The authority assigning the handicap also stipulates how it will be calculated. A common calculation that I've encountered is a percentage of the difference between a bowler's average & a target score, e.g. 90% of the difference between the bowler's average & 270.
To determine handicap you must first know your average. Take total number of games bowled and add the scores together. Then Divide by the total number of games bowled. For instance. Take the scores from three games of bowling and add them together. Then divide by three. This is your average bowling score (184 + 199 + 172 = 555. 555 / 3 = 185. Your average is 185).
Handicap Percentage is set in the bylaws of the league you joined. If you are unsure, ask your league secretary. The typical is 90% of 210/200. The number 210 represents the average game score across the league.
Take the average game score and subtract your average. Then multiply that number by the handicap percentage and you get your individual handicap. For example, if we take our average of 185 and subtract it from 210 we get 25. 90% of 25 is 22.5 or 23 pins of handicap (210 - 185 = 25. 90% of 25 or 0.9 x 25 = 22.5 which we round up to 23).