Rule 4 Calculator

What Is Rule 4 in Horse Racing?

Rule 4 (officially Rule 4(c) under Tattersalls Rules) is a deduction applied to winning horse racing bets when one or more runners are withdrawn from a race after bets have been placed. When a horse is declared a non-runner, it changes the competitive dynamics of the race — the remaining horses effectively have a stronger chance of winning. Rule 4 compensates for this by reducing the winnings on successful bets by a percentage based on the withdrawn horse’s starting price.

The deduction percentage is determined by the SP (starting price) of the non-runner at the time of withdrawal. The shorter the non-runner’s price, the more significant the impact on the remaining field, and therefore the larger the deduction. A horse withdrawn at odds of 1/9 or shorter carries the maximum 75p in £1 (75%) deduction, while a horse at 6/1 or longer carries no deduction at all.

How Are Rule 4 Deductions Applied?

The deduction is applied to your profit only, not to your returned stake. If you stake £10 on a winner at 4/1 (decimal 5.0) and a Rule 4 deduction of 20% applies, your calculation works as follows:

• Original profit: £10 × (5.0 − 1) = £40
• Deduction applied: £40 × 20% = £8
• Adjusted profit: £40 − £8 = £32
• Total return: £32 profit + £10 stake = £42 (instead of £50)

If multiple horses are withdrawn from the same race, the deductions are added together, up to a maximum of 75p in £1 regardless of how many non-runners there are. Our calculator handles multiple non-runners and caps the total deduction at 75% automatically.

When Does Rule 4 Apply?

Rule 4 applies when a horse is withdrawn after the race has been opened for betting — typically after declarations (approximately 48 hours before the race). If a horse is withdrawn before the race is open for betting, no Rule 4 applies as prices are simply recalculated without the non-runner. Rule 4 deductions are standard across all UKGC-licensed bookmakers when applied to bets struck before the non-runner’s withdrawal.

Important exceptions: Rule 4 does NOT apply to bets placed after the non-runner is officially declared, bets placed on exchanges (which simply adjust the market), or most ante-post bets (which typically have non-runner no bet terms). Check our horse racing betting guides for more on ante-post betting rules.

Rule 4 and Each-Way Bets

Rule 4 deductions apply equally to both the win and place parts of an each-way bet. The same percentage is deducted from the profit on each element. Place terms (the fraction of the win odds paid for a placed horse) are calculated on the original odds, then the Rule 4 deduction is applied to the resulting profit. Use our each-way calculator for standard each-way calculations without Rule 4 deductions, or the Rule 4 calculator above to factor in non-runners.

SP in Each-Way and Heinz Bets

Rule 4 deductions also apply to complex bets involving horse racing — including Heinz bets, Lucky 15s, and accumulators. In these cases, the deduction applies to each individual leg involving the relevant runner. Our calculator focuses on single bets, but the same percentage deductions apply to each affected leg within a multiple.

Do Bookmakers Apply Rule 4 Automatically?

Yes. All major UK bookmakers apply Rule 4 deductions automatically to affected bets when settling races. You do not need to calculate or request the deduction — it is applied as a standard part of the settlement process. Our calculator allows you to verify a bookmaker’s settlement or estimate your return before the race settles, particularly useful in big races where non-runners are common, such as the Grand National or Cheltenham Festival.