Horse racing deductions are cuts to your fixed odds when another runner is scratched after you've placed your bet. With a horse gone, everyone left has a better chance of winning, so the bookmaker takes a set number of cents in the dollar off your return. The shorter the scratched horse, the bigger the cut: a $2.00 favourite scratched can take 40c or more out of every dollar, while a $50 outsider usually costs you nothing. A deduction is fair when it roughly matches the scratched horse's real chance of winning, and you can check that with one division.
Big fields and late scratchings go together through the Spring Carnival, with Derby Day on Saturday 31 October and the Melbourne Cup on Tuesday 3 November 2026. Everything below uses invented numbers to show the method, not a view on any race or horse.
How a deduction works
You back a horse at $6.00 for $10, so your ticket's face value is $60. Later the favourite is scratched and a 20c deduction applies. Your return becomes $60 less 20c in every dollar, which is $48. In odds terms, your $6.00 is now $4.80.
Three things decide whether a deduction hits you:
- When you bet. Western Australia's Rules of Wagering apply the deduction to the face value of a bet made before the scratching became known. Bets placed after it are struck at the reformed prices, so no deduction.
- Which market. Deductions apply to final field markets, which open once the field is declared. Early futures bets are a different deal: if your horse doesn't run you lose, and nobody else gets a deduction.
- Fixed odds or tote. The tote has no deductions, because the pool reforms around the runners left. Our guide to tote vs fixed odds covers the rest of that difference.
If it's your horse that's scratched from a final field market, the bet is refunded.
Deduction tables: what bookmakers publish
Every bookmaker publishes its own schedule, keyed to the price of the scratched runner. Two public examples from Western Australia show the shape. The first is the Scale of Deduction Table in the state's Rules of Wagering 2005. The second is the schedule on PlayWest's help centre, an operator licensed by WA's Gaming and Wagering Commission.
| Scratched runner's price | WA rules: win | WA rules: place (8+ runners) | PlayWest: win | PlayWest: 3 places |
|---|---|---|---|---|
| $1.01 | 80c | 30c | 76c | 26c |
| $2.00 | 47c | 25c | 40c | 22c |
| $2.50 | 31c | 20c | ||
| $5.00 | 15c | 13c | ||
| $10.00 | 9c | 10c | ||
| $31.00 | 0c | 0c |
Blank cells are rows we haven't reproduced, not zeroes. The point is the pattern: two public schedules in one state give 47c and 40c for the same $2.00 scratching. Read your own bookmaker's terms, because that's the table your bet settles on.
Why place deductions are smaller
A place bet pays if your horse runs in the top two or three. Removing one rival only frees up part of one place, so your chance of placing rises less than your chance of winning. That's why the place column sits well under the win column for short-priced scratchings. Our post on each way betting covers how the place price itself is built.
What a fair deduction looks like
Here's the maths the tables are aiming at. If a runner with a fair chance of q is taken out, every other runner's chance grows in proportion, divided by (1 minus q). Your price is cut by the deduction, multiplied by (1 minus d). Put those together and your expected value doesn't change when d equals q.
So a fair deduction is the scratched runner's chance of winning with the margin removed, in cents.
Step 1: remove the margin
A $3.00 price implies 33.3%, but that includes the bookmaker's margin. Divide by the market percentage to get the fair chance. Our guide to market percentage in horse racing walks through it, and the calculators do it in seconds.
Invented example: the market adds up to 118%.
- The $3.00 favourite: 33.3% divided by 1.18 is a 28.25% fair chance.
- Your $8.00 runner: 12.5% divided by 1.18 is 10.59%.
Step 2: see what each deduction does
The favourite is scratched. Your runner's fair chance rises to 10.59% divided by (1 minus 0.2825), which is 14.76%. Here's your $20 bet at $8.00 under different deductions:
| Deduction | New price | Return on $20 | Expected value |
|---|---|---|---|
| None (before scratching) | $8.00 | $160.00 | -15.3% |
| 25c | $6.00 | $120.00 | -11.4% |
| 28.25c (fair) | $5.74 | $114.80 | -15.3% |
| 30c | $5.60 | $112.00 | -17.3% |
| 35c | $5.20 | $104.00 | -23.2% |
Expected value here is fair chance × price, minus 1. The -15.3% before the scratching is just the 118% market's margin.
What the table shows
- At the fair deduction, nothing changes. Your bet is worth the same before and after: you've paid the margin and nothing more.
- A deduction above fair costs you. At 35c, roughly 8 extra percentage points of expected value are gone.
- A deduction below fair helps you. At 25c the bet is worth more than it was.
- The verdict depends on the market percentage. A $2.00 runner is a 45.5% fair chance in a 110% market but only 40.0% in a 125% market. Against that range, a 47c deduction is on the heavy side, and 40c is about right only in a wide market.
This is a check, not a forecast. The maths assumes the scratched horse's chance spreads evenly across the field, which won't always be true. Take the only front runner out of a race and the pace changes, which can help some runners more than others.
Multiple scratchings
When two or more runners are scratched at once, WA's rules add the deductions together. Invented example: scratchings worth 20c and 13c make 33c, so your $8.00 becomes $5.36 and the $20 bet now returns $107.20. If the scratchings come at different times, what you pay depends on when you bet: a bet placed between them only takes the later one.
There's a floor, too. WA's rule for bookmakers says the payment after a deduction must be at least your stake and at least 20% of the ticket's face value. A $10 bet at $1.50 hit by a 76c deduction would work out at $3.60, but the floor lifts it back to $10, your stake.
Australian deductions vs the UK's Rule 4
If you read UK guides, watch the difference. A UK Rule 4 deduction comes off your winnings only, with your full stake returned. Under rules like WA's, the cents come off the whole face value, stake included.
| $10 at $5.00, 20c deduction | Calculation | Return |
|---|---|---|
| UK Rule 4 (winnings only) | $10 stake + ($40 × 0.80) | $42.00 |
| Face value (WA style) | $50 × 0.80 | $40.00 |
It's a small gap on one bet, but it means UK deduction tables and calculators won't match your Australian settlement.
Multis and dutching
- Multis. WA's rules cut the affected leg's price and recalculate the multi from the revised leg. A 30c cut on one leg cuts the whole multi by 30%.
- Dutching. One deduction hits every runner you've backed in that race, so your returns stay level but all shrink. Our guide to dutching has a worked example.
A quick checklist
- Check your bet is in a final field market, and placed before the scratching.
- Find the deduction in your bookmaker's schedule for the scratched runner's price.
- Work out the scratched runner's fair chance: 1 divided by its price, divided by the market percentage.
- Compare. If the deduction is well above the fair chance, it's costing you more than the scratching changed the race.
- Record the price you were actually paid, not the price you took, when you track your bets.
Compare fixed odds across bookmakers
Deductions only make sense against the market around them. BetBank's Racing Odds Screen shows live fixed odds for every runner across the major Australian bookmakers, with the best price highlighted and live fluctuations from market open to the jump, so you can see how a market reforms after a scratching. It's part of the Gold plan, with a 7-day free trial.
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