Rule 4 Calculator
A horse is withdrawn after you have taken a price, and your winnings come back smaller than you expected. This calculator applies the full Tattersalls Committee deduction scale to your bet — including the case where two horses are withdrawn and the 90 pence in the pound cap comes into play — and shows the price you effectively ended up with.
Fractional or decimal — both are accepted.
How the deduction is applied
Rule 4 reduces winnings, never the stake. Your profit is cut by the deduction, and the stake is returned in full on a winning bet. That is why the effective price falls but never below evens money on the stake itself.
Net return = stake + (stake × (odds − 1) × (1 − deduction))
Your bet after Rule 4
A worked example
You back a horse at 4/1 for £10 in the morning. An hour before the off, another runner priced at 5/1 is withdrawn. That horse falls in the 9/2 to 11/2 band, so the deduction is 15 pence in the pound.
Your bet wins. The full return would have been £50: £10 of stake and £40 of profit. The deduction takes 15% of the profit — £6 — leaving £34 of profit and a total return of £44. Your stake is untouched, and the price you effectively got was 3.4/1 rather than 4/1. Nothing has been taken from you arbitrarily: the field you were betting into changed after you took the price, and the deduction is the adjustment for it.
The scale is the withdrawn horse's chance, rounded down
The deduction table looks like an arbitrary list of bands. It is not. Convert the odds at the longer end of each band into an implied probability and round down to the nearest 5 pence, and you recover the published deduction in sixteen of the eighteen bands. The two exceptions, 2/5 to 1/3 and 4/5 to 4/6, land on a boundary and drop one step further — in the backer's favour, not against him.
That construction has a consequence nobody prints on the table. Because each band is priced at its longer end, a horse withdrawn near the shortend of a band is charged for less than its implied probability. The gap is the amount of the withdrawn horse's chance you are not being asked to pay for:
| Band | Charged | Implied at short end | Gap in your favour |
|---|---|---|---|
| Evens to 6/5 | 45p | 50.0% | 5.0p |
| 5/4 to 6/4 | 40p | 44.4% | 4.4p |
| 8/5 to 7/4 | 35p | 38.5% | 3.5p |
| 9/5 to 9/4 | 30p | 35.7% | 5.7p |
| 12/5 to 3/1 | 25p | 29.4% | 4.4p |
| 16/5 to 4/1 | 20p | 23.8% | 3.8p |
| 6/1 to 9/1 | 10p | 14.3% | 4.3p |
| 10/1 to 14/1 | 5p | 9.1% | 4.1p |
The largest gap on the scale is at 9/5, where the implied chance is 35.7% and the charge is 30 pence: 5.7 pence in the pound of the withdrawn horse's chance that the deduction does not collect.
One caveat matters more than the table itself, and most pages that reproduce the scale leave it out. An implied probability is not a true probability: the quoted price already carries the bookmaker's margin, and a typical race is priced to an overround of 10% to 20%. Deflate the implied figures by 15% and the picture evens out — the short bands turn about 1.5 pence against the backer while the long bands stay roughly 2 to 3 pence in his favour. Rule 4 is therefore close to fair overall, mildly generous when an outsider comes out and mildly harsh when a favourite does. It is not a charge invented to claw money back, which is the usual complaint about it.
Common questions
What is a Rule 4 deduction?
Rule 4 is the Tattersalls Committee rule that reduces winnings on a bet taken at a fixed price when a horse is later withdrawn or declared not to have started. Removing a runner makes the remaining runners more likely to win than the price you took reflected, so a deduction in pence in the pound is applied to your winnings to bring the bet back into line. It applies to the profit, never to the stake.
How much is deducted under Rule 4?
The deduction is set by the odds of the withdrawn horse at the moment of withdrawal, on a published scale running from 90 pence in the pound for a horse at 1/9 or shorter down to nothing at all above 14/1. A withdrawn horse at 4/1 costs 20 pence in the pound; at 6/1 to 9/1 it costs 10 pence. If two or more horses are withdrawn the deductions are combined, and the total can never exceed 90 pence in the pound.
Is Rule 4 taken off my stake as well as my winnings?
No. The deduction applies to winnings only, so your stake is returned in full on a winning bet. A £10 bet at 4/1 returns £50 normally, of which £40 is profit. A 20 pence deduction takes 20% off that £40, leaving £32 of profit and a total return of £42. Your effective price becomes 3.2/1 rather than 4/1.
Does Rule 4 apply if I took the starting price?
Not normally. Rule 4(c) is written for bets where a price was taken on the day of the race before the withdrawal. A starting price bet is settled at the price returned after the withdrawal has already been absorbed by the market, so there is nothing left to correct. Where a deduction is applied to an early price taken on a previous day, operators usually apply their own ante-post terms instead.
Why is the Rule 4 deduction not exactly the withdrawn horse's chance?
Because the scale works in bands and each band is set at the level of its longer-priced end, rounded down to the nearest 5 pence. A horse withdrawn at 9/5 implies a 35.7% chance but sits in the band that is charged 30 pence, so the deduction is 5.7 pence in the pound lighter than its implied probability, the largest gap on the scale. Against a true probability rather than an implied one the picture is more even, because the quoted price already contains the bookmaker's margin.
Sources and method
The deduction scale, the conditions under which Rule 4(c) applies and the 90 pence maximum are taken from the Tattersalls Committee Rules on Betting, read at source before publication rather than copied from a secondary table. Every implied probability, every gap in the table above and the overround adjustment were computed from the band odds and recalculated before publication.
Two limits, stated plainly. The scale is the Tattersalls standard and the great majority of UK operators apply it, but each operator settles under its own betting rules and those are the only binding terms for the bet in front of you — check them if a deduction looks wrong. And the 15% overround used in the discussion above is a representative figure for a competitive race, not a measurement of any particular market; bigger fields are priced fatter and the adjustment moves with them. This calculator covers win singles. Each-way bets have the deduction applied to the win and place parts separately — the each-way calculator handles the underlying returns, and the odds converter moves between fractional and decimal prices if you need to.
18+ only. This calculator settles arithmetic after the event; it does not predict results and nothing here is a selection. Betting should be entertainment you can afford to lose, never a way to make money. Set a deposit limit before you start and use it. If gambling is causing you harm, help is available — see our responsible gambling resources.