You can use a bonus bet on a multi only where the bookmaker's terms allow it, and when they do, a multi's longer price keeps more of a stake-not-returned bonus than a short single. With illustrative legs at $2.38, each fairly priced at $2.50, a $30 bonus bet averages $16.56 on one leg and $23.96 on a three-leg multi at $13.48. The stake the bonus never returns is a much smaller share of the bigger win.
The gain stops as the bookmaker's margin compounds with every leg, the chance of any return falls fast, and a multi cannot be laid on an exchange as one bet. Same game multis add a trap: when their legs pull the same way, they pay less than the legs multiplied.
Why a multi price keeps more of a bonus bet
A winning bonus bet pays only its winnings, bonus x (multi price - 1), as bonus bets explained sets out, and a multi pays only if every leg wins. For legs in different events, the multi price is the leg prices multiplied and the chance is the leg chances multiplied, so:
expected value = chance all legs win x bonus x (multi price - 1)
Example: Illustrative prices, not real events or a current offer. Each leg is a selection in a different race or game, priced at $2.38 by Bookmaker A against a fair price of $2.50, a 40% chance. You hold a $30 bonus bet. Multi prices are rounded to the cent, and the chance all legs win is 40% to the power of the number of legs.
| Legs | Multi price | Chance all legs win | A win pays | Expected value | Share of the $30 | Pays nothing |
|---|---|---|---|---|---|---|
| 1 | $2.38 | 40% | $30 x 1.38 = $41.40 | 40% x $41.40 = $16.56 | 55.2% | 60.0% |
| 2 | 2.38 x 2.38 = $5.66 | 16% | $30 x 4.66 = $139.80 | 16% x $139.80 = $22.37 | 74.6% | 84.0% |
| 3 | 2.38 x 2.38 x 2.38 = $13.48 | 6.4% | $30 x 12.48 = $374.40 | 6.4% x $374.40 = $23.96 | 79.9% | 93.6% |
| 4 | 2.38 to the power of 4 = $32.09 | 2.56% | $30 x 31.09 = $932.70 | 2.56% x $932.70 = $23.88 | 79.6% | 97.4% |
| 5 | 2.38 to the power of 5 = $76.36 | 1.024% | $30 x 75.36 = $2,260.80 | 1.024% x $2,260.80 = $23.15 | 77.2% | 99.0% |
The share kept climbs from 55.2% on one leg to 79.9% on three, then falls. Each leg is priced at 2.38 / 2.50 = 95.2% of fair, and the shortfall multiplies: the three-leg multi pays 13.48 / 15.625 = 86.3% of its fair price, the five-leg multi 76.36 / 97.66 = 78.2%. The rule is the one for a single: share kept = (multi price - 1) / fair multi price, here (13.48 - 1) / 15.625 = 79.9%. Multi bets explained shows how leg prices multiply and why the margin compounds.
Risk: Betting involves risk. A bigger share kept is an average, not a likely result: the three-leg multi in the table pays nothing 93.6% of the time. See responsible gambling for limits and support.
A multi or a single for the bonus
At the same price, a single carries one bookmaker margin and a multi one per leg. With an illustrative runner at $13.00 whose exchange price is $14.00, a $30 bonus bet keeps (13.00 - 1) / 14.00 = 85.7%, or $25.71, against $23.96 on the three-leg multi at $13.48. The advantage depends on the single's price being close to its exchange price: at $13.00 against $16.00 it keeps 12.00 / 16.00 = 75.0%, or $22.50.
Where the terms let you choose, look first for a long single close to its exchange price, which is also far easier to lay. Otherwise keep a bonus multi to a few legs close to fair. The best way to use bonus bets works the single-price sums.
Risk: Betting involves risk. A long single still loses most of the time (against an exchange price of $14.00, about 13 times in 14), and the exchange price is only an estimate. See responsible gambling for limits and support.
How fast the chance of a return falls
The last column of the table is the catch: the bonus pays nothing 60% of the time as a single and 93.6% on three legs. Across ten bonus bets on three-leg multis like the example, you would expect 10 x 6.4% = 0.64 winners, and the chance that all ten pay nothing is 0.936 to the power of 10 = 51.6%. On five legs it is 0.98976 to the power of 10 = 90.2%. The averages in the table are real, but they arrive as one large win among long runs of nothing.
A bonus bet puts no cash at risk; the danger is a losing run prompting cash multis to chase the big return.
Risk: Betting involves risk. A bonus bet that loses pays nothing, a long multi does that on most results, and an expected value only shows up over many bets. See responsible gambling for limits and support.
Laying a multi leg by leg, and what it costs
An exchange lists markets on each race or game, not on your combination of legs. The cover for a bonus multi is to lay the legs in turn, each before it starts: the first lay is sized off what the whole multi would pay, and each later one is larger.
Example: Illustrative prices. A $30 bonus bet on a double at $5.66, its two legs decided at different times. Each leg has an exchange lay price of $2.52, and the second is assumed to still be $2.52 when its turn comes. The commission rate is an illustrative 5%, written 0.05.
- If both legs win, the double pays $30 x (5.66 - 1) = $139.80.
- Lay the first leg: stake = $139.80 x 0.95 / ((2.52 - 0.05) x (2.52 - 0.05)) = $21.77, liability $21.77 x 1.52 = $33.09. If the first leg loses, this lay pays $21.77 x 0.95 = $20.68 and you are done.
- If the first leg wins, lay the second: stake = $139.80 / (2.52 - 0.05) = $56.60, liability $56.60 x 1.52 = $86.03. If it loses, you keep $56.60 x 0.95 - $33.09 = $20.68. If it wins, you keep $139.80 - $33.09 - $86.03 = $20.68.
Every path ends at $20.68, or 68.9% of the bonus, against a punting average of $22.37 on the double.
What the cover costs:
- Commission and the back-lay gap come off at every leg, so the cost compounds like the bookmaker's margin.
- The second lay's price is unknown until the first leg finishes, and if it moves, so does the amount you lock in.
- The liability grows as the multi survives: $86.03 on the second leg, on a $30 bonus.
- Legs decided at the same time cannot be laid in turn, and laying them all up front locks in nothing: at these prices, any lay leaves you behind on at least one of the results where one leg wins and the other loses.
- A same game multi has every leg in one game, and online bets on a sporting event in Australia must be placed before it starts (Interactive Gambling Act, s 8A(3) and s 10B). Every lay would go on before the game, against linked legs, so there is no clean way to convert one.
The bonus bet converter handles a single; for a multi, the sums above go leg by leg. The multi bet calculator works out a multi's combined price and return, and hedging a multi covers hedging its last leg.
Risk: Betting involves risk. Each lay has to be matched at the price you planned, a leg that is void, abandoned or settled differently at the exchange can leave you with an unequal result, and bookmakers' terms let them limit your stakes, void bets or close your account. See responsible gambling for limits and support.
The same game multi trap
A same game multi (SGM) takes all its legs from one game, and the legs are linked: a team that wins is more likely to have its forwards among the goals. The bookmaker prices that link, so an SGM whose legs pull the same way pays less than the legs multiplied, and the gap also carries the bookmaker's margin. How same game multi odds are calculated explains the correlation with numbers.
Example: Illustrative prices, not a real game. Three legs from one game are priced at $1.60, $1.90 and $2.10, which multiply to 1.60 x 1.90 x 2.10 = $6.38. The bookmaker prices them together as an SGM at $4.50.
A $30 bonus bet on that SGM wins $30 x (4.50 - 1) = $105.00, where the leg prices suggest $30 x (6.38 - 1) = $161.40. Read the bonus against the SGM price, not the legs. Even if $4.50 were a fair price for the three legs together, the bonus would keep 1 - 1 / 4.50 = 77.8% of its face value, or $23.33. The multiplied legs imply 1 - 1 / 6.38 = 84.3%. Any margin in the SGM price takes it lower still, and because no exchange prices that combination, you cannot measure by how much.
The terms that decide a bonus bet multi
Each bookmaker sets these for its own bonus bets, so read them before you build the ticket:
- whether a bonus bet can go on a multi at all, and on a same game multi;
- the minimum number of legs, and any minimum odds for each leg or for the whole multi;
- what happens when a leg is void, such as a player who takes no part in an SGM: removed and the multi re-priced, or the whole ticket void, and whether the bonus bet comes back;
- whether a multi placed with a bonus bet can also qualify for another promotion, such as multi insurance.
A void leg shortens the price: remove one leg of the $13.48 example and the ticket becomes a double at $5.66, paying $139.80 instead of $374.40. Betting promotions in Australia maps the other offer types and their rules.
Finding legs close to fair on B337's Terminal
Every sum here starts from a fair price for each leg. B337's Terminal lines up racing and sports prices from 40+ bookmakers with Betfair back and lay, price history (flucs), closing lines and EV overlays. Each overlay sets a price against an estimated fair price, taken from Betfair's own market for racing and, for sports, from a global market reference with the bookmaker margin stripped out. For legs on markets the board covers, checking them there first shows which sit closest to their estimated fair price.
Treat both fair prices as estimates. The board reads prices on a repeating cycle, so a number on screen may lag the bookmaker's site: check the live price in your bookmaker account before you bet. A free account opens a limited view of the Terminal with live odds; the Betfair columns and EV overlays begin at Terminal View, set out on plans and pricing. 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. A bonus bet multi pays nothing if any one leg loses, which on the five-leg example happens 99.0% of the time, and an EV overlay is an estimate, not a forecast. See responsible gambling for limits and support.