Rule 4 calculator

What Rule 4 does, and why it exists

When a declared runner is withdrawn after the final declaration stage — most commonly a veterinary scratching on the morning of the race, or a horse who blows the start and is formally withdrawn — the shape of the market changes. Whatever price you took earlier was, in part, a reflection of the other runners' chances. Remove one of them, and particularly if that one was fancied, the remaining horses all become a little easier to find. Tattersalls Rule 4(c) is the industry's way of taking account of this retrospectively.

The deduction is applied to winnings only, not to stake, and it is quoted in pence per pound. A 25p Rule 4 means that every pound of your winnings is reduced by twenty-five pence — a £100 winning return becomes £75. Your stake is always returned in full on top. The severity of the deduction scales with the odds of the withdrawn horse at the time of withdrawal: a withdrawn 2/1 second-favourite will trigger a much harsher cut than a 20/1 outsider whose absence barely troubles the book.

Two things worth knowing. First, if multiple horses are withdrawn before the race goes off, the deductions accumulate — two 25p reductions mean a total of 50p in the pound off your winnings, not 25p. The calculator handles that. Second, Rule 4 does not apply to bets placed after the withdrawal, since the reformed market will already have absorbed the change. It is the timestamp on your slip that matters, not the timestamp on the withdrawal.

In practice, Rule 4 tends to feel worse than it is because it lands as a surprise at settlement. A £20 each-way on a 5/1 shot with a 30p Rule 4 is still a perfectly acceptable result; it is just a less handsome one than it would have been. Best to factor the possibility in, particularly when backing against a short-priced favourite who might not make the start.