AFL Expected Value Calculator
Enter the price on offer for an AFL match, your own estimate of the win probability and a stake, and get the expected value of the bet in dollars and as a percentage of stake.
EV Calculator
Inputs
Enter a fair price or a percentage, whichever your estimate is in.
The decimal price the bookmaker is quoting.
Your own price for the outcome, before any margin.
Results
Positive expected value: +10.00% of stake
The price of 2.20 is longer than the fair price of 2.00 implied by your probability.
- Expected value
- +10.00%
- Expected profit
- +$10.00
- Win probability
- 50.00%
- Break-even strike rate
- 45.45%
- Profit if it wins
- $120.00
- Loss if it loses
- $100.00
- Full Kelly stake
- 8.33%
- Quarter Kelly stake
- 2.08%
As a percentage of stake
Average result per bet at this price
Fair price 2.00
Implied by the price on offer
Percentage of bankroll
Percentage of bankroll
| Kelly fraction | Stake, share of bankroll |
|---|---|
| Full Kelly | 8.33% |
| Half Kelly | 4.17% |
| Quarter Kelly | 2.08% |
Expected value is a long-run average, not a forecast of this bet. The figure is only as good as the probability you supply, and moving that estimate a couple of points can flip the sign. The Kelly stakes assume the probability is exact, which it is not, so most people stake a fraction of full Kelly.
How the AFL Expected Value Calculator works
Expected value is the average result of a bet if it could be repeated many times at the same price with the same true probability. It weighs the profit you make when the bet wins against the stake you lose when it does not, then adds the two together. A positive number says the price is longer than your estimate of the chance; a negative number says the price is shorter.
The output is only as good as the probability you feed it. The calculator does not know the true chance of an AFL result, so the probability input is yours to supply, whether from a model, from a devigged market, or from your own read. Change the probability by a couple of points and the EV can flip sign, which is the honest signal that the estimate, not the arithmetic, is doing the work.
EV = (probability x (decimal odds - 1) x stake) - ((1 - probability) x stake) EV % = EV / stake x 100
Example
A price of 2.50 with a 45.00% win probability and a $100 stake gives an expected value of +$12.50, or +12.50% of stake. The bet wins $150 profit 45 per cent of the time and loses $100 the other 55 per cent, so 0.45 x $150 = $67.50 against 0.55 x $100 = $55.00.
How to use it
- Enter the decimal odds on offer, for example 2.50.
- Enter your own estimate of the win probability as a percentage, for example 45.
- Enter the stake you would place, for example 100.
- Read the expected value in dollars and as a percentage of stake.
AFL Expected Value Calculator FAQ
What counts as a good EV percentage?
There is no universal threshold, because the number scales with how confident you are in the probability input. A 1 per cent EV derived from a sharp closing line is a very different thing to a 15 per cent EV derived from a hand estimate on an AFL player prop. Many people who bet to a model treat anything under 2 or 3 per cent as inside the error band of their own estimate and ignore it. Larger figures are worth a second look at the probability rather than the price.
Where should the win probability come from?
The most common sources are a rating model, a devigged market price, or a base rate from historical data. Devigging a sharp market is the simplest starting point: take the prices from a market you trust, strip out the margin, and use the resulting probability as your estimate. If you use the same bookmaker for both the probability and the price you are checking, the EV will always come out negative by roughly the margin, because you are comparing a price against itself.
Does positive EV mean the bet will win?
No. Expected value is a long-run average, not a prediction about a single result. A bet with a 45 per cent chance at 2.50 has positive expected value and still loses more often than it wins. The variance around that average is large, and a run of losing bets is entirely consistent with a positive edge. This is why staking method matters as much as price selection, and why bankroll sizing tools such as the Kelly calculator exist alongside EV.
How does EV relate to the bookmaker margin?
A bookmaker margin is the reason the average bet has negative expected value. If a two-way market holds a 4 per cent margin and both prices are fair relative to true probability, backing either side returns roughly minus 2 per cent EV. Positive EV therefore requires the price you take to be longer than the true probability by more than the share of margin sitting on that side. The margin calculator shows how much is being held on a given market.
Should I use EV in dollars or EV as a percentage?
Percentage is the better comparison between bets, because it removes stake size and lets you rank opportunities on the same scale. Dollars are the better figure for planning, because they tell you what the bet is actually worth adding to your book. A 5 per cent edge on a $20 bet and a 1 per cent edge on a $200 bet are worth the same dollar amount, but the first is a far stronger signal about the price and the second is more exposed to a small error in your probability.
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