AFL Devig Calculator
Enter the prices from an AFL market and get the fair prices and probabilities with the bookmaker margin removed, using whichever of the four devigging methods you prefer.
Devig Calculator
Inputs
Methods agree on an even market and diverge sharply at long odds.
Every outcome in the market has to be entered, or the margin removed will be too small.
Results
3.91% of margin removed by the multiplicative method
Divides each implied probability by the book total. Spreads the margin in proportion to price.
- Book percentage
- 103.91%
- Margin removed
- 3.91%
- Outcomes devigged
- 2
Implied probabilities summed
Book percentage less 100%
Fair probabilities always sum to 100%
| Outcome | Bookie odds | Implied probability | Fair probability | Fair odds |
|---|---|---|---|---|
| Outcome 1 | 1.90 | 52.63% | 50.65% | 1.97 |
| Outcome 2 | 1.95 | 51.28% | 49.35% | 2.03 |
A devigged price is the market price with the margin removed, not a true probability. It reflects what the bookmaker believes, how the money has landed and any position being managed. On a lopsided market the four methods disagree by an amount large enough to change a value claim, so treat the fair price on an outsider as approximate.
How the AFL Devig Calculator works
Every bookmaker price contains a margin, so the implied probabilities on both sides of a market add to more than 100 per cent. Devigging removes that excess and rescales both sides so they sum to exactly 100 per cent, producing the probability the market is effectively quoting once the margin is stripped out.
This calculator uses the multiplicative method, which divides each implied probability by the total. It assumes the margin is spread across both sides in proportion to their price, which is the standard starting point. Other methods, such as additive or power devigging, distribute the margin differently and give noticeably different answers at long odds, so the fair price on a heavy outsider should always be treated as approximate.
Total implied = 1 / odds A + 1 / odds B Fair probability A = (1 / odds A) / total implied Fair odds A = 1 / fair probability A
Example
A two-way market priced 1.90 and 1.95 has implied probabilities of 52.63% and 51.28%, summing to 103.91%. Devigging gives fair probabilities of 50.65% and 49.35%, which are fair prices of 1.97 and 2.03. The margin removed is 3.91%.
How to use it
- Enter the decimal price on the first side of the market, for example 1.90.
- Enter the decimal price on the other side, for example 1.95.
- Read the fair probability and fair price for each side.
- Compare the fair price against what another bookmaker is offering.
AFL Devig Calculator FAQ
What is a devigged price used for?
It is the most common way to build a probability estimate without a model of your own. Take a market you consider sharp, strip out the margin, and use the resulting probability as your estimate of the true chance. You can then price the same event at another bookmaker and see whether it is longer than fair. The whole approach rests on the first market genuinely being sharper than the second, which is an assumption you should be able to defend.
Which devigging method should I use?
The multiplicative method used here is the default and is close to adequate for even markets such as AFL line and total bets. Where the two sides are far apart, methods diverge: multiplicative assigns proportionally more margin to the favourite, while additive splits the margin evenly and the power method assigns more to the outsider. For long shot prices such as anytime goal scorer markets the choice can change the fair probability by a relative margin large enough to matter.
Why does devigging matter more on long odds?
Because the margin is a much larger share of a small probability. Removing 4 percentage points of total margin from a market split 90 to 10 changes the favourite by a fraction of a per cent in relative terms, but changes the outsider substantially. That is where the method you pick starts to dominate the answer. It is also why value claims on long shot markets built from a devigged favourite-heavy market should be treated with real caution.
Can I devig a market with more than two outcomes?
Yes, the multiplicative method extends directly: sum the implied probabilities of every outcome and divide each one by the total. This calculator covers the two-way case, which is what AFL head-to-head, line and total markets are. For markets with many outcomes, such as a premiership futures market, the same arithmetic works but the margin is typically far larger and unevenly distributed, so the fair prices are much rougher estimates.
Is a devigged price the true probability?
No. It is the market probability with the margin removed, which is a different thing. It reflects what a bookmaker believes plus how the money has landed plus any position they are managing. Devigging a sharp market is a reasonable proxy for true probability because such markets are hard to beat, but devigging a soft market just gives you a clean version of a poor estimate. The quality of the source market is what determines the quality of the output.
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