No-Vig Calculator

Devigging means removing the bookmaker’s margin from a market to see the prices underneath — the “fair” or “no-vig” odds.

Every market is priced so the implied probabilities add to more than 100%. A −110 / −110 line implies 52.38% on each side, 104.76% in total, and the 4.76% excess is the book’s. Devigging scales those figures back to 100% so what is left is the market’s actual estimate rather than its estimate plus its fee.

It is how a sharp book’s line becomes a probability you can price your own bets against.

Every price a sportsbook offers is shaded in its favour. Add up the implied probabilities of all the outcomes and you get more than 100%: a −110 / −110 market implies 52.38% twice over, or 104.76% in total. The 4.76 points of excess are not a forecast of anything. They are the fee.

Removing them is called devigging, and the standard method is proportional: divide each outcome’s implied probability by the market total so the set sums to exactly 1. Each side keeps its share of the market’s opinion, and only the margin is stripped. In the example above, 52.38 / 104.76 = 50% each, and the fair price is +100 on both sides.

The result is the most useful number in betting: an estimate of the true probability, sourced from the market rather than from you. Take the no-vig probability from a sharp book — one with high limits and thin margins — and you have a benchmark. Any other book offering longer odds than that fair price is offering value, and the size of the gap is the size of your edge. This is what most disciplined bettors actually do instead of handicapping games themselves.

Proportional devigging is not the only method — the multiplicative and Shin approaches distribute the margin differently, on the theory that books load more of it onto longshots. They diverge most on lopsided markets. For balanced two-way lines the difference is small, and the proportional method used here is the one to learn first.

A market priced −140 / +120. Decimals are 1.714 and 2.20, implying 58.33% and 45.45%. The total is 103.79%, so the hold is 3.79 / 103.79 = 3.65%.

Devigged: 58.33 / 103.79 = 56.20% and 45.45 / 103.79 = 43.80%, which sum to 100. The fair prices are 1 / 0.562 = 1.779 (about −128) and 1 / 0.438 = 2.283 (about +128).

Now the payoff. If another book is offering +140 on that underdog, you are being paid at 41.67% for something the sharp market says is 43.80% — a real edge of just over two points. That is what a value bet looks like, and it is invisible until the vig is removed.

What does devigging actually do?

It rescales the implied probabilities of a market so they add to exactly 100%, removing the bookmaker’s margin. What is left is the market’s estimate of the true chance of each outcome.

Which book should I devig?

The sharpest one you can find — a high-limit, low-margin book whose prices move first. Devigging a soft book gives you that book’s opinion with its fee removed, which is not the same as a fair estimate of the outcome.

Do I need every outcome?

Yes. Margin is a property of the whole market, so a partial market cannot be devigged. For soccer that means all three of home, draw and away.

Is proportional devigging the best method?

It is the standard and the simplest, and it is fine for balanced markets. On heavy favourites it may understate the longshot’s true price, since books tend to load extra margin there — the multiplicative and Shin methods address that.

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