Rule 4 Calculator: Check Horse Racing Returns After Non-Runners

A Rule 4 calculator works out how much a withdrawn horse reduces the winnings on a fixed-odds horse racing bet. Most returns calculators ignore it, so a winning bet can pay less than the screen promised. The method is simple: find the deduction from the withdrawn horse’s price, take it off winnings only, then add your stake back.

What does a Rule 4 calculator do?

A Rule 4 calculator cuts the winnings on a winning bet by a set number of pence in the pound, based on the price of a horse withdrawn after you struck your bet. Rule 4 is the common name for Rule 4(C) of the Tattersalls Committee Rules on Betting, the industry-standard deduction for non-runners.

The logic is fair to both sides. When a horse is pulled out, every remaining runner is more likely to win, so a price taken earlier becomes too generous. William Hill’s help page explains that bookmakers re-price new bets if there is time, but must adjust returns on bets already placed that go on to win.

The deduction is quoted in pence in the pound. A 25p deduction means you lose 25p of every £1 of winnings, or 25%. Your stake comes back in full.

Which price sets the Rule 4 deduction?

The deduction comes from the price of the withdrawn horse at the moment it came out, not from the horse you backed. The shorter the non-runner’s price, the bigger the deduction.

The table below is the standard Tattersalls scale as published consistently by several UK racing guides, such as Got The Odds. Your bookmaker’s own rules settle your bet, so check them if a figure looks off.

Three practical points. A price that falls between bands goes into the next one up: Betfair’s Sportsbook help gives 21/5 as an example treated as the 9/2 band. If a calculator asks for decimal odds, subtract 1 to get the fractional price (a withdrawn horse at 4.0 is 3/1). And some online bookmakers do not apply the 5p band at all, so a 10/1 to 14/1 non-runner may cost you nothing; OLBG’s guide flags this.

The most common mistake: using your own horse’s price

You back a 10/1 winner with £10. The 2/1 favourite is withdrawn, which sits in the 15/8 to 9/4 band and costs 30p in the pound.

• Correct: winnings £100 less 30% = £70, so the total return is £80.
• Wrong (using your own 10/1 price, a 5p band): winnings £100 less 5% = £95, so you would expect £105.

That is a £25 gap from one wrong input, which is why the withdrawn horse’s price is the first thing to check.

How do you calculate a Rule 4 deduction by hand?

Work out the winnings, apply the deduction to the winnings only, then add the stake back. Doing it in that order stops the two most common errors: deducting from the stake and adding the stake twice.

Worked example. You back a horse at 4/1 with a £10 win bet. A 3/1 shot is later withdrawn, which falls in the 25p band.

• Winnings before deduction: £10 × 4 = £40
• Rule 4 deduction: £40 × 0.25 = £10
• Adjusted winnings: £30
• Total return: £30 + £10 stake = £40
• Profit: £30

As a formula: total return = stake + winnings × (1 − deduction). The bet that looked like a £50 return now pays £40.

A shortcut for any returns calculator

Multiply the fractional odds by (1 − deduction) and use the result as your new price. A 4/1 shot with a 25p deduction becomes 3/1, and a 10/1 shot with a 30p deduction becomes 7/1. Enter that adjusted price into a normal returns calculator and it will match the Rule 4 figure, for win bets, each-way bets and each leg of a multiple.

Our betting tools page lists the other calculators. Expect a one-penny gap from your settled bet, because bookmakers round at different stages.

How does Rule 4 apply to each-way bets?

Rule 4 applies to the winnings on both parts of an each-way bet, at the same rate. Calculate the win part and the place part separately, then deduct from each.

Worked example. You place £5 each-way (£10 in total) at 10/1 with one-quarter place terms. A 5/1 shot is withdrawn, so the deduction is 15p in the pound, and your horse wins.

• Win part winnings: £5 × 10 = £50, less 15% = £42.50
• Place part odds: 10/1 × ¼ = 5/2, so winnings are £5 × 2.5 = £12.50, less 15% = £10.625
• Total return: £10 stakes + £42.50 + £10.625 = £63.125

Without Rule 4 the same bet returns £72.50. The extra half-penny shows why a calculator and a settled bet can differ by a penny.

Withdrawals can also change the place terms. William Hill’s rules say the number of runners is based on the horses that took part in the race, so a small field after withdrawals can mean fewer places. Our guide to extra-place races covers how enhanced place terms work.

How does Rule 4 work in doubles and accumulators?

In a multiple bet, the deduction applies only to the leg containing the affected race. The other legs run at their full odds. William Hill’s terms say that in multiples the deduction only applies to parts of the bet involving the withdrawn horse.

Worked example. A £10 double, with Horse A at 3/1 and Horse B at 2/1. Without any withdrawal it returns £10 × 4 × 3 = £120. Now a horse is withdrawn from Horse A’s race, with a 25p deduction.

• Leg A returns £1 × (1 + 3 × 0.75) = £3.25 per £1 staked
• Leg B is untouched at 3.0 (decimal)
• Total return: £10 × 3.25 × 3 = £97.50

For longer accumulators, adjust each affected leg separately. Our free bet profit calculators guide is a useful companion when a bonus bet is involved, as those have their own stake rules.

What if more than one horse is withdrawn?

Deductions from separate non-runners are added together, and the Tattersalls rule says the total shall not exceed 90 pence in the pound. So you always keep at least 10p of every £1 of winnings.

For example, withdrawals at 3/1 (25p) and 11/2 (15p) combine to 40p. On £40 of winnings, that takes £16 off and leaves £24.

Now take an unusual race with withdrawals at 2/1 (30p), Evens (45p) and 6/4 (40p). That adds up to 115p, so the 90p cap applies: £40 of winnings becomes £4, and a £10 stake returns £14.

The same rule covers reformed markets. When bookmakers form a new market after the first withdrawal, a further withdrawal can add to the deduction on bets taken in the original market, with the total calculated on original-market prices. Bets placed in the new market are judged on that market’s prices.

How are Betfair Exchange reductions different?

Betfair Exchange uses a reduction factor, not the Tattersalls scale, and it works on the matched price rather than on winnings. In a win market, the new price is the matched price minus (price ÷ 100 × reduction factor).

Betfair’s own worked example is a £10 back bet at 8.6 when a horse with a 16.2% reduction factor is withdrawn.

• Price reduction: 8.6 ÷ 100 × 16.2 = 1.39
• New price: 8.6 − 1.39 = 7.21
• Profit falls from £76.00 to £62.10, and total return from £86.00 to £72.10

Because the decimal price includes your stake, a 16.2% factor cuts profit by about 18%, slightly more than the headline figure. Win-market reductions under 2.5% are not applied. In place markets, Betfair applies the factor to winnings directly: £70 of winnings with a 25% factor becomes £52.50.

When does Rule 4 not apply?

Rule 4 does not apply to bets placed after a new market forms, to bets on the non-runner itself (stakes are returned), or to exchange bets in the same form. Check which case your bet falls under before you trust a calculator’s figure.

• Bets struck after a new market forms. The withdrawal is already in the price you took.
• Starting price (SP) bets. William Hill says Rule 4 usually only applies if you took a price, though a very late withdrawal can affect an SP bet. Read the terms for yours.
• Walkovers. If withdrawals leave only one runner, the Tattersalls rules void all bets on the race.
• Ante-post bets. A bet on a horse that never runs is normally a loser, not a Rule 4 case, unless the bookmaker’s ante-post terms say otherwise.
• Pool betting. Tote-style payouts come from a shared pool, not from fixed odds.

How do you check a calculator’s answer?

Compare five inputs with your bet slip, then redo the sum by hand. A calculator can be arithmetically perfect and still answer the wrong question.

1. Stake, selection and the odds you accepted, not the current price.
2. Bet type: win, each-way, SP, double or accumulator.
3. Price of each withdrawn horse at withdrawal and the band it falls in.
4. Whether your bet was struck before the withdrawal or in a new market.
5. Whether the figure shown is winnings, total return or profit.

If your settled bet shows a different figure, look at the settlement screen. It should show the deduction applied, and the bookmaker’s rules say which scale they used. The gap is usually rounding or a different withdrawal time, not an error.

Before you place the next bet

Treat any horse racing returns figure as provisional until declarations are final and no further runners can be withdrawn.

Frequently asked questions

How do I calculate a Rule 4 deduction?

Multiply your winnings by the deduction in pence in the pound (for example 25p = 0.25), subtract that from the winnings, then add your stake back. A £10 bet at 4/1 with a 25p deduction returns £40, not £50.

Does Rule 4 reduce my stake?

No. The deduction comes off winnings only, and your stake is returned in full on a winning fixed-odds bet.

What is the Rule 4 deduction if a 2/1 favourite is withdrawn?

A horse withdrawn at 2/1 falls in the 15/8 to 9/4 band, which carries a 30p-in-the-pound deduction on the standard Tattersalls scale. Check your bookmaker's rules to confirm.

Is there a maximum Rule 4 deduction?

Yes. The Tattersalls rule says that when two or more horses are withdrawn, the total reduction cannot exceed 90p in the pound.

Does Rule 4 apply to each-way bets?

Yes, to the winnings on both the win and place parts, at the same rate. The place terms themselves may also change if the field shrinks.

Does the Betfair Exchange use Rule 4?

No, not in the same form. It applies a reduction factor to the matched price for both backers and layers, which works differently from the Sportsbook scale.