A horse
came out.
Now what?

A betting market is priced so that the implied probabilities of all the runners add up to rather more than 100%. Withdraw a runner and that horse's share of the probability has to go somewhere — it spreads across everything still in the race. Every surviving bet becomes better value than the price it was struck at.

Rather than reprice bets that have already been taken, the rules claw the difference back with a flat deduction from winnings. The size of it is read off a nineteen-band scale against the withdrawn horse's price at the moment of official notification — not its price that morning, and not its price at the off.

The arithmetic is one line. Your stake never enters it:

return = stake + profit × (1 − deduction ÷ 100)

So £10 at 4/1 makes £40 of profit. A 3/1 non-runner sits in the 25p band, removing a quarter of that profit — £10 — and leaving £30. Add the stake back and the bet returns £40. If you want the undeducted figure to compare against, the payout calculator gives you that, and the odds converter will turn a fractional price into decimal if your bookmaker quotes one and your slip shows the other.

Two or more withdrawals add up rather than compound. Three horses out at 2/1, 4/1 and 12/1 give 30p plus 20p plus 5p — 55p in the pound. Compounding them would give 46.8p, which is the wrong answer and a common enough mistake to be worth stating plainly.

Whatever the total comes to, Rule 4(C) caps it: the reduction "shall not exceed 90 pence in the pound". The calculator flags the cap when it bites.

Starting Price bets. Normally exempt — SP is struck after the market re-forms, so it already accounts for the withdrawal. The exception is where there was too little time to form a new market, in which case the same scale applies.

Ante-post bets. Outside Rule 4(C) altogether, which is scoped to prices taken on the day of the race. Ante-post bets carry their own risk instead: they usually lose if your selection never runs.

Bets into an already-reformed market. If the market re-formed after a withdrawal and you bet into it afterwards, that withdrawal is already in your price and does not deduct. Only a subsequent one would.

Walkovers. If withdrawals leave one runner, all bets on the race are void — refunded, not deducted.

The scale, the 90p cap and the exemptions above are taken from the Tattersalls Committee's Rules on Betting, Rule 4(C) and Rule 10(b). The Committee has issued these rules since 1886; the current version was last revised on 17 May 2010 and is the one displayed at British racecourses. The Gambling Commission does not write the scale — it requires licensed bookmakers to follow it unless they display a differing rule prominently.

Every band on this page was checked against that document directly rather than copied from another calculator. Bookmaker-specific variations — the reported waivers of the smallest 5p band, and the separate reduction-factor mechanism betting exchanges use — are deliberately not encoded, because we could not verify them against the bookmakers' own published rules. Our methodology page explains how we source and check formulas generally.