The single most common profitable-sounding bet that isn't, in AU bookmakers, goes like this: pick four heavy favourites at $1.20 each. Multi them together. The combined odds are roughly $2.07. You're effectively betting $100 to win $107 on four events where each individual event is an 83% favourite. What could possibly go wrong?
A lot, it turns out. This is a short piece because the maths is short. Once you see the actual numbers, the bet never looks attractive again.
The true probability
Four favourites at $1.20 each. If each $1.20 price accurately reflects probability, the implied probability per leg is 1/1.20 = 83.3%. The probability of all four winning is 0.833^4 = 48.2%.
Fair odds for an event with 48.2% probability are $2.07. Which is what the bookmaker is offering. Sounds fair, right?
Except the implied probability of 83.3% per leg already includes the bookmaker's margin. A $1.20 favourite at an AU corporate typically has a true probability closer to 80%. The 3.3% difference is the vig on that single leg.
True probability across four favourites at 80% each: 0.80^4 = 40.96%.
Fair odds for a 40.96% probability event: 1/0.4096 = $2.44.
You're being offered $2.07 for an outcome whose fair price is $2.44. You're paying about 15% vig on that multi. On a $100 stake, your expected loss is around $15 per placement.
Why it feels like a good bet
The psychological pull is obvious. Four favourites. They're all supposed to win. The $2.07 payout is a small premium over your stake, but a guaranteed-looking premium. Four straight coin-flip favourites feel almost dishonest to be wary of.
The maths doesn't care how they feel. 48.2% of the time, all four favourites win and you collect $207 on a $100 stake. 51.8% of the time, at least one loses and you lose the full $100. Expected value: (0.482 × $207) + (0.518 × -$100) = -$2.20 per bet on the assumption of fair prices, and much worse once you account for the actual vig.
The mental trap is that each individual leg feels like a safe bet, and we don't naturally multiply independent probabilities. A 17% chance of failure per leg doesn't feel meaningful. Over four legs, the cumulative failure probability is 52%. The bet is more likely to lose than to win, and when it loses, it loses everything.
The doubling-down trap
The next move after a losing favourites multi is often a bigger favourites multi the following week. “I was unlucky. Four favourites lose less than half the time. It'll hit soon.” This is where real money gets lost.
The problem is that the vig compounds across attempts. Every multi you place is paying roughly 15% edge to the bookmaker. Ten attempts at $100 each: expected loss of $150 before variance. Twenty attempts: expected loss of $300. The “sure thing” multi is a 15% tax on your bankroll per placement, and each time you don't hit, the hole gets deeper.
There's no version of this that turns profitable. The underlying events are priced with vig. Multiplying vigged prices compounds the vig. Arithmetic, not opinion.
What about boosted versions
Some AU bookmakers offer boosted odds on favourite-heavy multis as promos. “Boost this 4-leg favourite multi by 20%.” The boosted price on our example becomes $2.48 - slightly above fair value of $2.44.
This is genuinely +EV, but the bookmaker knows it. Boosts on favourite multis are almost always capped ($50 max stake, for example), limited to one per customer per week, and available only on specific pre-selected multis rather than ones you build yourself. The total dollar value extractable from these boosts across a year is small - maybe $200-500 - and hitting them aggressively correlates with getting flagged for account limiting.
If a boost is available, hit it. Don't build a strategy around them, and don't bet favourite multis at the unboosted price because the unboosted price is a large negative expected value.
What about correlation
The calculation above assumes the four matches are independent events. In practice some multi-leg structures include correlated outcomes - four Saturday AFL favourites where the same public-money flow might be pushing all four prices.
Correlation can cut either way and is hard to price precisely without a model. Without getting into the weeds, the practical answer is that correlation in multis of favourites on the same weekend is typically mild, and not enough to move the expected-value calculation from negative to positive at unboosted prices. The bet remains a losing proposition regardless.
A fair comparison
If you genuinely think those four favourites are going to win, the bet to place is four separate singles. $25 on each favourite at $1.20.
Possible outcomes:
- All four win: $100 × 0.20 per leg = $20 profit (collecting $120 total).
- Three of four win: $90 collected on $100 staked = $10 loss.
- Two of four win: $60 collected on $100 staked = $40 loss.
- One of four wins: $30 collected on $100 staked = $70 loss.
- None win: full $100 loss.
The upside is smaller, but the variance is dramatically lower. Expected value on the singles structure is approximately -$4 (from the compounded single-leg vig), vs -$15 on the multi structure. The singles are almost four times more efficient for the same exposure to the same four events.
The longer piece on multis covers the same logic for +EV multis where you believe you have an edge on every leg. The short version is that singles dominate multis for bankroll efficiency in almost every case.
The summary
Four favourites at $1.20 each combined into a $2.07 multi is paying roughly 15% vig for the privilege of compressing your outcomes into an all-or-nothing structure. There is no structural advantage to the multi form. The bookmaker loves it because it's one of their highest-margin products. The punter loves it because the short-odds framing feels safe. The maths doesn't love it at all.
If you want to bet four favourites, bet them singly. The expected value is meaningfully better, the variance is dramatically lower, and you get to keep collecting on each individual win rather than losing the whole stake when one of four backs get unlucky. It's less exciting. It's also not a mathematical disaster.
Tom has been punting in Australia long enough to have strong opinions about most of it. Writes the opinion column — multis, Betfair, why your mate is wrong about betting, and the cultural side of being a sharp AU punter.