No-vig odds calculator

What the no-vig number actually is

A sportsbook does not post the probability it believes in. It posts a price it can make money on regardless of the result. If you add up the implied probabilities on both sides of any two-way market, the total comes to more than 100 percent. That surplus is the hold — the built-in margin the book keeps for making the market. Removing it is the first honest thing you can do to a line.

The arithmetic, step by step

Convert each American price to an implied probability. A negative price of −140 becomes 140 ÷ (140 + 100), or 58.33 percent. A positive price of +120 becomes 100 ÷ (120 + 100), or 45.45 percent. Added together those come to 103.79 percent. The extra 3.79 points do not belong to either team — they belong to the book.

To remove them, divide each side by the total. 58.33 ÷ 103.79 gives 56.20 percent, and 45.45 ÷ 103.79 gives 43.80 percent. Those two now sum to exactly 100. That pair is the market's real opinion once the fee is taken out, and it is the number you should be comparing your own estimate against — never the raw posted price.

Why this is the only fair comparison

Suppose your model says a team wins 57 percent of the time and the price is −140. The raw implied number is 58.33 percent, so it looks like you have no bet. Strip the vig and the market is really at 56.20 percent, which means your 57 is a genuine, if small, disagreement. The opposite happens just as often: an edge that looked large against the raw number evaporates once the juice comes out. Betting against un-adjusted prices systematically overstates how often you are right.

What the hold tells you about the book

Hold is the cleanest measure of how expensive a market is. A standard −110 / −110 point spread holds about 4.5 percent. Sharp books running reduced juice can sit near 2 percent. Live in-game markets, exotic props and long-shot futures regularly run 6 to 20 percent, and every point of hold is a point you have to overcome before you break even. Two books can show the same headline number and charge very different amounts for it.

Where this method stops working

Proportional de-vigging assumes the margin is split evenly between the two sides. On lopsided markets — heavy favourites, long-shot props — books load more of the hold onto the long shot, so the true fair price on the favourite is slightly better than this calculator shows. For markets with three or more outcomes, the same divide-by-the-total step works, but the distortion grows. Treat the output as a good estimate, not a measurement.