Handicap racing is based on the tried-and-tested notion that increasing the amount of weight that a horse carries in a race, relative to its rivals, will ultimately slow it down. In Britain, when a horse has run three, or possibly fewer, times, it is allocated an official handicap rating by the British Horseracing Authority (BHA) handicapper. The official handicap rating expresses, in Imperial pounds, the perceived ability of the horse in the eyes of the handicapper and, in a handicap race, determines the weight the horse carries, subject to any weight allowance claimed by its jockey. Thus, in a handicap race for horses officially rated 81-100, if the highest weight to be carried is 9st 12lb a horse rated 93 would carry 9st 5lb, one rated 89 would carry 9st 1lb, and so on.
Handicap races, which comprise 60% of the horse races run annually in Britain, are intended to give each and every horse an equal chance of winning, at least in theory, thereby creating a competitive betting market and an exciting spectacle for spectators. Handicap ratings are reviewed race-by-race and may increase, decrease or remain unaltered, depending upon the performance of the horse in question. For example, if a horse wins a race, it is an entirely reasonable deduction that the horse has run better than its current official handicap rating to do so, so a rise in the weights, typically 6lb or 7lb, but possibly more, is warranted. Conversely, if a horse runs poorly, a fall in the weights may be appropriate, although the handicapper is likely to require confirmation, from two, three or more substandard performances, before taking any action.