Devig Calculator
Remove bookmaker margin from any market — recover the true probabilities and fair odds. Power, Multiplicative, Additive and Shin methods.
| Outcome | Bookie odds | Implied prob | Fair prob | Fair odds |
|---|---|---|---|---|
| Outcome 1 | 1.91 | 52.36% | 50.00% | 2.000 |
| Outcome 2 | 1.91 | 52.36% | 50.00% | 2.000 |
How the devig calculator works
Bookmakers bake a margin (the "vig" or "overround") into every market. If you sum the implied probabilities of every outcome, the total exceeds 100% — the excess is the book's edge. Devigging redistributes that excess back to the outcomes so the probabilities sum to exactly 100%.
The four methods
- Multiplicative — divide every implied probability by the total overround. Simple, fast, equal-margin assumption.
p' = p / S. - Additive — subtract
(S − 1) / nfrom each implied probability. Distributes the vig equally in probability space. Can produce negative outputs on heavy favourites — floored then renormalised. - Power — find exponent
ksuch thatΣ pik = 1. Compresses favourites less aggressively than multiplicative and is the academic default for 2-way markets. - Shin — solves for the proportion
zof informed bettors the book is defending against, then derives fair probabilities. Most theoretically motivated; best for markets with sharp action.
How to interpret the result
The fair odds column is your benchmark line. If an AU bookmaker offers higher decimal odds on the same outcome, the bet is +EV; if lower, the book has the edge. Always devig a sharp book (Pinnacle, Circa) — devigging a soft book just gives you back the soft book's opinion minus its margin.
FAQ
- What is devigging and why do bettors do it?
Devigging strips the bookmaker margin (overround) out of a posted market so the remaining probabilities sum to exactly 100%. The result is an estimate of the "true" probability of each outcome. Sharp bettors devig a sharp book like Pinnacle, then compare those true probabilities against the prices at AU soft books to find +EV bets.
- When should I use a devig calculator?
Any time you want to convert a sharp posted price into a probability estimate. Common uses: building a true-line for +EV scanning, sanity-checking your own model against the market, deriving fair odds for a market where you have no model, or comparing two soft books to see which is closer to fair.
- Power vs Shin — which method should I use?
Power is the academic default for 2-way markets (NFL spreads, MLB moneylines, tennis H2H) — it preserves the rank order and handles favourite-longshot bias reasonably. Shin is the most theoretically motivated for markets with informed-trader risk (player props, futures, horse racing) but is harder to calibrate. Multiplicative is fine for tight 2-way markets where margin is low. Additive is rarely correct but useful as a sanity check.
- Why is Pinnacle considered the gold standard for devigging?
Pinnacle runs a low-margin (~2-3%), high-volume sportsbook that welcomes sharp action and adjusts lines aggressively to incoming bets. Their closing line is treated by academic studies as the most accurate single estimate of true probability in sports betting. Devigging a Pinnacle price gets you very close to a fair line. Circa Sports is the US equivalent for some markets.
- Are devig outputs the absolute truth?
No. Devigging is an estimate — it assumes the bookmaker has priced the market efficiently and the only adjustment needed is removing margin. In reality, even sharp books have edge in less-liquid markets (props, futures, lower-tier sports). Treat devigged fair odds as a strong baseline, not gospel. The further a bookmaker is from being sharp, the worse the devig estimate.
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