An odds boost is a promotion that raises the price a bookmaker pays on a bet: it swaps the price for a higher one, adds a percentage to the winnings, or multiplies the whole price. A boost is worth taking only when the boosted price beats the fair price, the price with the bookmaker's margin taken out. A bet boosted from an illustrative $2.88 to $3.20, on a selection whose fair price is $3.00, is worth 3.20 / 3.00 - 1 = 6.7% of the stake on average.
The headline percentage does not show that. The same 25% is worth different amounts on different prices, and a stake cap or a bonus bet payout can take most of the value away. In NSW a boosted price offered beside the normal price counts as an inducement, which limits how bookmakers may advertise one.
What an odds boost does to the price
Three shapes of boost turn up in Australian accounts. On an illustrative selection at $2.88:
| Shape | What changes | Boosted price on $2.88 |
|---|---|---|
| Odds boost (a price boost or boosted special) | The bookmaker replaces the price with a higher one it names | $3.20 |
| Profit boost (a winnings boost), here 25% | The winnings rise by the percentage: 1 + (price - 1) x 1.25 | 1 + 1.88 x 1.25 = $3.35 |
| Price multiplier, here 10% | The whole price, stake included, is multiplied: price x 1.10 | 2.88 x 1.10 = $3.168 |
A boost can be a token you apply to a bet you choose, or a market the bookmaker has boosted, and the extra can be paid in cash or as a bonus bet. Betting promotions in Australia covers the other promotion types.
Bonus odds is not a defined term in betting rules: treat an offer sold as bonus odds as a boost and find which of the three shapes its terms describe.
Profit boost vs odds boost: the same 25% is not worth the same
With illustrative prices, a head to head market has the favourite at $1.44 and the underdog at $2.88, a market percentage of 1 / 1.44 + 1 / 2.88 = 2 / 2.88 + 1 / 2.88 = 3 / 2.88 = about 104.2%. Because $2.88 is exactly twice $1.44, removing the margin in proportion leaves the favourite a fair chance of two-thirds, a fair price of $1.50, and the underdog one-third, a fair price of $3.00. How to calculate fair odds covers this and the other sources of a fair price, and the fair odds calculator takes the margin out of a whole market.
Expected value = chance x stake x price - stake, so on a $50 bet the favourite's sums take 2 / 3 of the return and the underdog's take 1 / 3:
| Boost | Favourite at $1.44 (fair $1.50) | Underdog at $2.88 (fair $3.00) |
|---|---|---|
| None | 2 x $50 x 1.44 / 3 - $50 = -$2.00 | $50 x 2.88 / 3 - $50 = -$2.00 |
| Odds boost to a named price | $1.52: 2 x $76.00 / 3 - $50 = +$0.67 | $3.20: $160.00 / 3 - $50 = +$3.33 |
| 25% profit boost | 1 + 0.44 x 1.25 = $1.55: 2 x $77.50 / 3 - $50 = +$1.67 | $3.35: $167.50 / 3 - $50 = +$5.83 |
| 10% price multiplier | 1.44 x 1.10 = $1.584: 2 x $79.20 / 3 - $50 = +$2.80 | $3.168: $158.40 / 3 - $50 = +$2.80 |
What the table shows:
- A bet at a named boosted price is worth boosted price / fair price - 1 per dollar: 1.52 / 1.50 - 1 = 1.3% on the favourite, against 6.7% for $3.20 on the underdog.
- A profit boost multiplies only the winnings, so the same 25% is worth more on the longer price.
- A multiplier scales the stake too, so at the same margin it adds the same share anywhere. Both prices sit at 96% of fair (1.44 / 1.50 and 2.88 / 3.00), so a bet with the 10% multiplier is worth 1.10 x 0.96 - 1 = 5.6% of the stake on either.
A profit boost beats the margin only if it lifts the price to fair. Break-even boost = (fair price - 1) / (price - 1) - 1, which is 0.50 / 0.44 - 1 = 13.6% on the favourite and 2.00 / 1.88 - 1 = 6.4% on the underdog. A 10% profit boost therefore loses value on the favourite: 1 + 0.44 x 1.10 = $1.484, worth 2 x 1.484 / 3 - 1 = -1.1%. On the underdog it adds value: 1 + 1.88 x 1.10 = $3.068, worth 3.068 / 3 - 1 = +2.3%.
Risk: Betting involves risk. A boost with positive expected value is an average over many bets, and the underdog here still loses two times in three, boost or no boost. See responsible gambling for limits and support.
Boosted price vs the fair price
The fair price can come from:
- the bookmaker's own market with the margin removed, as above, which suits two-way and three-way markets;
- a betting exchange, for racing and the larger sports markets, once commission is allowed for;
- your own estimate, which is only as good as the work behind it.
Edge = boosted price / fair price - 1, and expected value = edge x stake. With illustrative prices, a runner boosted from $5.00 to $5.50 when the exchange puts it at about $5.80 is still worth 5.50 / 5.80 - 1 = -5.2%: the boost made a losing bet lose less. Value betting applies the same test without a boost, and the guide to valuing a betting promotion works a boost against exchange prices.
Risk: Betting involves risk. A boosted price above fair still loses every time the selection loses, and a fair price is an estimate, not a known chance. See responsible gambling for limits and support.
Maximum stake caps and payout limits
Depending on the terms, a stake above the cap is refused, or split so only the capped part is boosted. With the 25% profit boost on the $2.88 underdog and $100 to bet, a winner returns $288 plus a boost of $100 x 1.88 x 25% = $47 (illustrative terms):
| Terms on the $100 bet | Working | Expected value |
|---|---|---|
| No cap, extra paid in cash | ($288 + $47) / 3 - $100 | +$11.67 |
| Extra paid as a bonus bet worth 72 cents in the dollar | ($288 + 0.72 x $47) / 3 - $100 | +$7.28 |
| Extra winnings capped at $20 | ($288 + $20) / 3 - $100 | +$2.67 |
| Stake capped at $50, the other $50 at $2.88 | +$5.83 + ($50 x 2.88 / 3 - $50) | +$3.83 |
The 72% is an assumed value for the bonus bet. At $200 against the $50 cap, the other $150 is a plain bet worth $150 x 2.88 / 3 - $150 = -$6.00, turning the boost's +$5.83 into -$0.17.
Risk: Betting involves risk. The bookmaker decides whether a bet qualifies for a boost, so a bet placed for the boost can end up paid at the normal price. A bonus bet that loses pays nothing. See responsible gambling for limits and support.
Boosts on multis and same game multis
A boost on a multi works against a margin that compounds with each leg. With illustrative legs each fair at $2.00 and offered at $1.92 (96% of fair), and multi prices rounded to the cent:
| Legs | Multi price | Fair price | Expected value per $1 | With a 20% profit boost |
|---|---|---|---|---|
| 3 | 1.92 x 1.92 x 1.92 = $7.08 | $8.00 | 7.08 / 8.00 - 1 = -11.5% | 1 + 6.08 x 1.20 = $8.296: +3.7% |
| 5 | 1.92 x 1.92 x 1.92 x 1.92 x 1.92 = $26.09 | $32.00 | 26.09 / 32.00 - 1 = -18.5% | 1 + 25.09 x 1.20 = $31.108: -2.8% |
The boost adds the same share of the winnings at any length, while the multi keeps less of its fair value with each leg. So the break-even boost climbs: at five legs it is (32.00 - 1) / (26.09 - 1) - 1 = 23.6%.
A boost on a same game multi starts from a price already cut for linked legs, so multiplying the legs' fair prices gives no fair price for it. Same game multi promotions shows how to estimate the chances on an SGM.
Risk: Betting involves risk. A boosted multi still loses if any one leg loses: five legs with a 50% chance each all win only one time in 32. See responsible gambling for limits and support.
How NSW law treats odds boosts
In NSW, the Betting and Racing Act 1998 defines an inducement to include the offer of a gambling product with additional benefits or enhancements (s 33GA). Section 33H makes it an offence to publish or communicate an inducement to gamble, or to gamble more often. Liquor & Gaming NSW's regulatory position of 9 October 2020 treats advertising special odds, meaning more than one price for the same outcome, as advertising an inducement. A single price offered over the course of a market, even one sold as a special, counts as ordinary odds, which may be promoted.
Liquor & Gaming NSW's guideline GL4015 lists special odds or increased winnings for a limited period, a specific race or match, or a minimum bet amount among the offers it treats as prohibited when made to the world at large. Special odds or increased winnings on a whole sport or round that let a customer bet at all times are not treated as prohibited where they do not persuade or encourage anyone to gamble, or to gamble more often (checked October 2026). That carve-out does not cover bonus bets. Certain offers can still go directly to account holders who have agreed to receive them. Other states, the national framework and the Commonwealth's 2026 reforms, most of which start on 1 January 2027, add their own rules, which betting inducement rules in Australia sets out.
Note: Rules checked 7 October 2026. This is general information, not legal advice, and it describes boost shapes, not any current offer.
Mistakes that cost money with odds boosts
| Mistake | What it costs |
|---|---|
| Judging the boost against the old price | $2.88 to $3.20 looks like 3.20 / 2.88 - 1 = 11.1% more, but against the fair $3.00 the bet is worth 6.7% |
| A profit boost on a short price | With 10% on the $1.44 favourite the bet is worth -1.1% |
| Staking past the cap | $200 into a $50 cap turns +$5.83 into -$0.17 |
| Counting a bonus bet payout as cash | +$11.67 becomes +$7.28 on the $100 example, $4.39 overstated |
| Betting only because a boost arrived | Without the boost, each $50 bet here is worth -$2.00 |
Skip a boost when:
- the boosted price is still below fair;
- the market has no fair price you can work out, such as a novelty market or a long SGM;
- its minimum stake is more than you planned to bet;
- the offer is the only reason you are betting.
How to stop betting promotions covers opting out of offers.
Risk: Betting involves risk. These costs are averages over many bets, not what any one bet pays. See responsible gambling for limits and support.
Checking a boost against fair prices on B337's Terminal
B337's Terminal shows racing and sports prices from 40+ bookmakers side by side, with Betfair back and lay, price history (flucs), closing lines and EV overlays. The overlays compare each price with an estimated fair price: Betfair's own market for racing, and for sports a global market reference with the bookmaker margin removed. Weigh a boosted price against the same reference with the edge test above.
Both references are estimates. The Terminal reads prices on a repeating cycle and shows each one as at the time displayed, so check a boosted price in your bookmaker account before you bet. A free account opens a limited view of the Terminal with live odds; Betfair prices and EV overlays start with Terminal View, and plans and pricing lists each plan. Bookmaker names are trade marks of their owners. B337 is not affiliated with them.
For free and confidential support call 1800 858 858 or visit gamblinghelponline.org.au.
Risk: Betting involves risk. An EV overlay is an estimate, not a forecast, a bet priced above it can lose several times in a row, and a bookmaker can limit your stakes or close your account under its terms. See responsible gambling for limits and support.