# How does betting work, and how do the numbers add up?

> How fixed-odds betting works in Australia: decimal odds, implied probability, margin, multi bets and expected value, with illustrative worked examples.

Source: https://bookiechecklist.com/how-betting-works/
Updated: 2026-11-13

Fixed-odds betting turns a price into a payout: stake times decimal odds. The same price implies a probability, and the prices across a market add up to more than 100%, which is the margin. This hub explains odds, multi bets, margin and expected value with worked examples, all marked illustrative, and points to the calculators.

## The three numbers

**Return.** Stake times decimal odds. A$20 at 2.50 returns A$50.00, which is A$30.00 profit plus the A$20 stake.

**Implied probability.** One divided by the odds. At 2.50 that is 0.40, or 40%.

**Margin.** Add the implied probabilities across a market and subtract one. Two outcomes priced at 1.90 each give 52.63% plus 52.63%, or 105.26%, so a margin of 5.26%.

*Illustrative example, not a price.*

**The upshot:** price, implied probability and margin are the same arithmetic seen three ways.

## Multi bets

A multi bet combines legs, and the odds multiply. Three legs at 1.80 each combine to 1.80 × 1.80 × 1.80 = 5.832. A$10 returns A$58.32.

One lost leg loses the whole bet. *Illustrative example, not a price.*

## Expected value

Expected value is stake × (your probability × odds − 1). With odds of 3.00 and your own estimate of 30%, the result is 0.9 − 1 = −0.10 per A$1 staked. The estimate is yours, not a fact.

The arithmetic only shows what the estimate implies.

*Illustrative example, not a price.* The calculators on this site use the same formulas and are for education.

**The upshot:** the formula is simple; the estimate you feed it decides everything.

## Where the limits are

Online in-play betting on sport is banned. Credit cards and digital currency are banned for betting. Both rules are explained on [licensing and legality](https://bookiechecklist.com/licensing-and-legality/) and [paying a bookmaker](https://bookiechecklist.com/paying-bookmakers/).

Tools to stay in control are on [staying in control](https://bookiechecklist.com/staying-in-control/).

## 18+ and where to get help

18+ only. Gambling can be harmful. Need help? Call Gambling Help Online on 1800 858 858 (free, 24/7) or visit [gamblinghelponline.org.au](https://www.gamblinghelponline.org.au/). To exclude yourself from licensed Australian online and phone wagering providers, register with BetStop at [betstop.gov.au](https://www.betstop.gov.au/). BetStop help line: 1800 238 786.

## FAQ

**How do decimal odds turn into a payout?**

Multiply the stake by the odds. A$20 at 2.50 returns A$50.00, including the stake.

**What is a bookmaker's margin?**

The amount by which the implied probabilities across a market exceed 100%. Two outcomes at 1.90 give 105.26%, a margin of 5.26%.

**What happens to a multi bet if one leg loses?**

The whole bet loses. The odds of the legs multiply, so the payout is higher, but every leg must win.