When Rule 4 is on your side
Most people meet Rule 4 as a deduction from their winnings. But the deduction is a fixed amount for a price, not a measure of what the withdrawal did to your horse's chance. When the chance goes up by more than the deduction takes away, Rule 4 is a help.
A worked example
Invented numbers to show the arithmetic. Not a forecast and not betting advice.
Three runners. Horses A and B are both evens. Horse C is 200/1 and is only there to make up the numbers. Before the off you have £1,000 on B at evens.
- A runs. A and B share the race about equally. B wins about half the time. At evens, that is a fair bet and your expected return is about £1,000 for every £1,000 staked.
- A is withdrawn. Your bet was struck before the withdrawal. A was evens, so the deduction is 45p in the £ of your winnings (see the scale). B now faces only C, so B wins about 99 times in 100. If it wins, your £1,000 profit becomes £550, and your £1,000 stake comes back as well: £1,550 in all.
So after the deduction you are being paid 11/20 about a horse that wins nearly every time. That is worth about 1.53 times the fair return. In expected-return terms that is a gain of about 53% on the stake.
How big is that, in prices?
Punters think in prices, and a gain of about 53% in the odds sounds modest until it is put the way a price looks. Each row below has about the same gain: you are paid the price in the first column about a horse that is really worth the price in the second.
Everyday size
6/1 about a 7/2 shot
Decimal 7.0 against 4.5, a ratio of 1.56.
Headline size
25/1 about a 16/1 shot
Decimal 26.0 against 17.0, a ratio of 1.53.
| Paid | Really worth | Gain in expected return |
|---|---|---|
| 2/1 | evens | +50% |
| 6/1 | 7/2 | +56% |
| 16/1 | 10/1 | +55% |
| 25/1 | 16/1 | +53% |
| 33/1 | 21/1 | +55% |
Big prices can mislead the other way too: 20/1 down to 10/1 looks like a similar move to 2/1 down to evens, but it is a much bigger change (decimal 21 against 11, a ratio of 1.9, against 3 against 2, a ratio of 1.5). Compare the decimal prices, not the fractions.
Why it is not a sure thing
- You cannot know a horse will be withdrawn. Withdrawals are rare, and most are announced to everyone at the same moment. If you bet on B expecting A to come out and A runs, you have bet at about the fair price or worse, with a bookmaker's margin on top.
- The break-even chance can be small. If evens is a fair price for B, the break-even chance of a withdrawal is close to zero; if your price was 10% worse than fair, a withdrawal has to happen in about 1 race in 6 for the bet to pay on average. The calculator below does the sum for any numbers.
- Prices move. Where a withdrawal is likely, the price on B usually shortens before it happens, so the chance to take evens may not last. And a bet struck after a new market has formed is not hit by a withdrawal already made.
- A single bet can lose. A 99% chance still loses 1 time in 100.
- A walkover voids the bet. If only one runner is left, bookmakers void the bets. That is why the example needs a third horse.
- Acting on private information is a different matter. Backing a horse because someone with inside knowledge told you the other would not run is not what this page is about. The Tango Sky story shows how seriously that is treated.
Try your own numbers
The calculator works out the break-even: how likely a withdrawal has to be for your bet to pay on average. The chances are your own estimates. The pre-filled figures are the example above with a price 10% worse than fair.
The short version
- Rule 4 takes a fixed slice of your winnings; it does not know how much better your horse's chance has become.
- When one of two joint favourites goes, the other's chance rises a lot and the deduction is only 45p or so: that is the case where Rule 4 can help.
- When a long-priced horse goes and the deduction is 5p or nothing, there is no real effect either way.
- Never bet more than you can afford to lose. A bet with an edge can still lose.