Rule 4 is one of those betting rules that seems to appear from nowhere, quietly shrinking your winnings after a horse race. In reality it is a fair adjustment with a clear purpose, and once you understand it you will never be caught out by a reduced payout again.
The rule applies when a horse is withdrawn from a race after betting has opened but too late for the market to be fully reformed. This guide explains why the deduction exists and how it is calculated.
Why Rule 4 Exists
When a horse is withdrawn, the remaining runners all become more likely to win, so the odds you took earlier are now too generous. Rather than resettle the whole market, bookmakers apply a proportional deduction to winning bets to reflect the removed runner's chance.
How the Deduction Is Calculated
The size of the deduction depends on the odds of the withdrawn horse at the time it was pulled out. The shorter the withdrawn horse's price, the bigger its implied chance, and the larger the deduction. Deductions are expressed as pence in the pound of your winnings.
General Pattern
A short-priced withdrawn favourite leads to a larger deduction, sometimes a substantial share of your winnings, while a longshot withdrawal may lead to little or no deduction at all. Bookmakers publish standard Rule 4 tables mapping the withdrawn horse's odds to a deduction rate.
What Rule 4 Applies To
The deduction applies to your winnings, not your stake, and only to bets placed before the withdrawal at the affected odds. If you took a price after the market was reformed, Rule 4 typically does not apply to that bet.
Rule 4 in the Calculator
The Bet Calculator Betmentor includes a Rule 4 option so you can apply a deduction and see your adjusted return. This is especially handy for each-way bets, where the deduction affects both parts of the bet.
A Calm Approach to Deductions
Rule 4 is not a bookmaker taking liberties; it is a standard, published adjustment that keeps payouts fair after a late withdrawal. Knowing it exists, and modelling it before you celebrate a win, keeps your expectations accurate. It sits alongside dead heat rules as one of the settlement adjustments every racing bettor should know.