A no-vig calculator tells you what a line would look like if the book took nothing. Take a game priced -150 / +130. Add up the implied chances and you get 103.5%, not 100%: that extra 3.5% is the vig. Strip it out and the fair line is about -138 / +138. If another book is offering +140 on the underdog, you now know that’s a better-than-fair price. The free calculator above does that for two-way and three-way markets, with three different ways of removing the margin.
How the no-vig calculator removes the vig
Every method starts the same way: turn each price into an implied chance (1 ÷ decimal odds). Where they differ is how they share out the overround.
- Multiplicative divides every chance by the total. Simple, and what most people mean by “no-vig odds”. It assumes the book loaded the margin evenly in proportion to each price.
- Additive takes the same flat amount off every outcome. It treats a 5% favourite and a 90% favourite equally, which is rarely how books price things, and it can push a big longshot below zero. The calculator warns you when it does.
- Power raises every implied chance to the same power k, solved so they add to exactly 100%. That takes proportionally more off longshots, which matches the favourite-longshot bias you see in most real markets.
On a near 50/50 game the three methods barely disagree. On a 1.20 / 5.50 tennis match they can be a full percentage point apart on the outsider, and that’s enough to flip a small edge.
Testing a price
Tick “Test a price”, type the odds you can actually get, and the calculator shows your edge against the fair line. It’s the core of what people call positive-EV betting: de-vig a sharp market, then look for softer books paying more than that fair price. The catch is that the fair line is only as good as the market you took it from. De-vig a book with a 9% margin and slow lines and you’ll find “value” everywhere that isn’t really there.
For a single line’s margin and break-even rate, the vig calculator is quicker. To turn your fair chance into a stake, try the Kelly criterion calculator, and to judge bets after the fact the CLV calculator compares your price with the close.
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