What Is Rule 4 in Horse Racing?

Non-runners are part of the sport. Horses get withdrawn for all sorts of reasons - injury or illness, poor or unsuitable track conditions - and when that happens, the complexion of the race changes as well. The industry-standard Rule 4 exists to account for that.

Here's exactly what it means, how deductions are calculated and what it means for your bet.

What is Rule 4 in horse racing?

Rule 4 - formally the Tattersalls Rule 4 - is applied when a horse is withdrawn from a race after bets have been placed. With fewer runners, the remaining horses have a better chance of winning, and so a deduction is made to reflect that shift. It applies to win, each-way and derivative markets and is a rule that all bookmakers follow.

At Bally Bet, Rule 4 deductions are calculated based on the odds of the horse at the moment it is scratched (withdrawn) from our markets.

When do Rule 4 deductions apply?

Deductions are applied when a horse is withdrawn from a race and there is time for the market to be recalculated. If a withdrawal happens just before the race and there is not enough time to form a new market, the Rule 4 deduction is applied to the starting price (SP) of the remaining runners instead.

It's also worth noting that dead heat rules and Tattersalls Rule 4 deductions apply to all win, each-way and derivative markets.

Final declarations - the point at which the field is confirmed and Rule 4 becomes applicable - typically close 24-48 hours before a race, though for some major events this window can extend further. The Grand National, for example, operates on a 72-hour declaration window.

How we calculate Rule 4 deductions

The deduction amount depends on the odds of the withdrawn horse at the time of withdrawal. The shorter the price, the bigger the impact on the race, and so the larger the deduction. A withdrawn favourite will carry a significantly higher deduction than an outsider.

Deductions are calculated based on the table below, available in both decimal and fractional formats, which applies to win and each-way markets.

Where a decimal price has no direct fractional equivalent, we reserve the right to apply Tattersalls Rule 4 deductions based on the decimal table.

If a withdrawn horse is priced at 10/1 or higher, no deduction is applied. A 5% deduction is also exempt, so if a calculation produces a 5% figure, no deduction is applied at that level.

To work out your recalculated odds after a deduction, the formula is: (odds minus 1) divided by 100, multiplied by (100 minus the deduction), then add 1. For example, if your bet was placed at decimal odds of 13.0 (12/1) and a runner is withdrawn at 3.25 (9/4), a 30% deduction applies. The calculation would be (13.0 - 1) / 100 * 70 + 1 = 9.40.

Rule 4 in action: a worked example

Say you back Horse A at 5/1 in a five-runner race. Before the off, Horse B - priced at 7/4 - is withdrawn. The race now has four runners, and your selection's chance of winning has increased. The 5/1 you took no longer reflects that reality, so a deduction is applied to your winnings to compensate.

Using our deductions table above, a horse withdrawn at 7/4 falls in the 2.60–2.79 range, which carries a 35% deduction. That deduction is applied to your winnings, not your stake.

The maximum Rule 4 deduction

The maximum deduction that can be applied is 90%, regardless of how many horses are withdrawn from a race.

Multiple withdrawals and Rule 4

Multiple deductions can apply if more than one horse is withdrawn. Each withdrawal carries its own deduction based on that horse's odds at the time it was scratched, and the deductions are combined, up to the 90% cap.

In races with reserves, Tattersalls Rule 4 deductions apply to all runners, except where a reserve fails to qualify for the race. If a reserve gains entry to the field due to withdrawals and is later withdrawn itself, Tattersalls Rule 4 deductions will still apply.

Is my stake returned with Rule 4 deductions?

Yes. Rule 4 deductions are only applied to winnings, so your stake is returned in full. The exception is where a dead heat also applies alongside a Rule 4, in which case dead heat rules would affect the stake calculation as well.

Rule 4 and ante-post betting

Tattersalls Rule 4 deductions do not apply to ante-post markets. Dead heat rules do still apply to ante-post bets.

Rule 4 in greyhound racing

Rule 4 deductions apply to greyhound racing in the same way as horse racing. If a greyhound is withdrawn from a race after bets have been placed, a deduction is applied to reflect the improved chances of the remaining runners.

The deduction is calculated based on the odds of the withdrawn greyhound at the moment it is scratched from our markets, using the same table as horse racing. The same 90% maximum applies, and the 5% exemption remains in place.

As with horse racing, if a withdrawal happens just before the race and there is insufficient time to reform the market, the deduction is applied to the starting price (SP) of the remaining runners. Dead heat rules and Rule 4 deductions apply to all win, each-way and derivative markets in greyhound racing.

How do I check if Rule 4 has been applied to my bet?

With us, the quickest way is to head to the My Bets section of your Bally Bet account.

If Rule 4 has been applied, you'll see a Rule 4 label attached to the relevant bet. Tap it to see the deduction amount - for example, '25p in the £ deduction is applied' - along with a link to further information on how the deduction has been calculated.

Check out our Terms & Conditions in full for further information about Rule 4 deductions and other general betting rules.

Interested in more horse racing betting explainers like this? Make your way to the Bally Bet blog for the latest sports betting guides and event overviews sitting alongside our online casino tips and game recommendations.

All offers mentioned correct at the time of writing but may be subject to change.