How to calculate the probability of a 10-team parlay hitting

A ten-team parlay, commonly called a ten-leg multi in Australia, lands only when all ten selections are correct. It can contain ten strong favourites and still be a long-priced bet because every additional leg creates another opportunity for the accumulator to fail.

The calculation begins with multiplying individual win probabilities, but a credible estimate must also account for bookmaker margins, related selections and settlement rules. That makes the maths more useful than judging each leg separately and calling the ticket “safe”.

The basic maths behind a ten-leg parlay

Label the ten selections from 1 to 10, with estimated win probabilities of (p_1, p_2, \ldots, p_{10}). If the outcomes are independent, the probability that every leg wins is:

(P(\text{hit}) = p_1 \times p_2 \times \cdots \times p_{10})

When every selection has the same probability, the calculation becomes (p^{10}). A 60% chance on each leg produces a combined chance of approximately 0.60¹⁰, or 0.60%, before considering whether the selections are genuinely independent.

Decimal odds provide a market-based starting point. The combined parlay price is (O = o_1 \times o_2 \times \cdots \times o_{10}), and the implied probability from that combined price is (1/O). Individual decimal odds also convert to implied probabilities using (1/o), although bookmaker margins mean these are not perfectly fair estimates.

A ten-favourite example

Suppose all ten selections are offered at decimal odds of 1.50. Each price implies a 66.67% chance, so multiplying the ten implied probabilities gives:

((1/1.50)^{10} = 1.734%)

That is roughly one chance in 58. The combined odds would be (1.50^{10} = 57.665), meaning a $10 stake would return about $576.65, including the stake, if every selection won.

The 1.734% figure also represents the break-even rate at those quoted prices. If research suggests each selection actually has a 60% chance, the estimated parlay probability falls to 0.60¹⁰, or about 0.60%. The combined odds would remain unchanged, but the bet would then have a negative expected value.

Where the simple formula needs adjustment

Bookmaker prices contain a margin, so their implied probabilities normally add to more than 100% across all possible outcomes. A simple no-margin estimate can be obtained by dividing one outcome’s implied probability by the sum of all implied probabilities for that market. Even that remains a market estimate rather than an objective truth.

Ten different teams do not guarantee independence. A match result and a team-scoring proposition can be closely related, while weather, rest and referee assignments may affect several football or cricket selections at once. Where outcomes are dependent, the calculation should use conditional probabilities: the probability of the second leg given the first result, and so on.

Settlement rules also matter. A push or void can reduce the number of active legs, while an abandoned cricket match or a drawn NRL game may be settled according to the particular sportsbook’s terms. AFL’s rare grand-final draw, which can lead to a replay, illustrates why the rules attached to each market deserve close attention.

Australian markets and local betting realities

Australian sportsbooks generally use decimal odds and stakes in Australian dollars, while betting exchanges display back and lay prices that can be converted into equivalent probabilities. Local betting language includes “multi”, “leg” and “when it lands”, with phrases such as “getting on” also widely understood.

Aussie punters commonly build multis around the AFL, NRL, A-League Men, Super Rugby, the Big Bash and international cricket or football. Melbourne’s cold, wet winters and Perth’s dry heat can influence scoring markets, while games in Sydney and Brisbane may reach Perth in the small hours. Those time differences can also determine whether late team news is available before a leg begins.

Online betting in Australia is provided through operators licensed by state and territory regulators or approved onshore racecourses. The federal ACMA framework prohibits click-to-call wagering, while individual state rules govern licensing and consumer protection. Comparing the decimal prices, same-game multi options and settlement policies across the Australian market is therefore part of calculating a realistic price.

Building a defensible probability estimate

Start with each selection’s most likely outcome rather than the outcome that merely produces the longest parlay. Market prices, team ratings, injuries, expected line-ups, weather and recent form can then be combined into an individual probability. Remove the bookmaker margin where possible and use the highest-quality estimate available for every leg.

Next, check whether selections share relevant information and apply the sportsbook’s push, void and draw rules. A cash-out quote is the price offered to close the remaining exposure; it is not the same as the probability of the original parlay landing. Promotions and betting credits can improve expected value in particular circumstances, but they do not change the underlying chance of winning.

The number to remember is that a ten-leg parlay’s probability is the product of its component probabilities, adjusted for dependence and market conditions—not the sum of their apparent confidence.