Betting math
FreeNo-Vig / Fair Odds
Sportsbook prices on both sides of a market add up to more than 100%. The extra is the book's margin (the vig). Remove it to see the market's fair probability for each side.
Market odds (American)
Fair (no-vig) odds
Enter the odds for every side of the market.
How this works
Raw implied probability of each side = 1 / decimal odds.
Sportsbook hold = (sum of raw implied probabilities) − 100%. −110 / −110 → 52.38% + 52.38% − 100% = 4.76%. (The book's theoretical margin on a perfectly balanced book, 1 − 1/sum, is 4.55% for the same market.)
No-vig probability uses standard proportional normalisation: pA no-vig = pA / (pA + pB). The same method extends to three-way markets: each side ÷ the sum of all sides.
Fair odds are the American odds of the no-vig probability. Proportional removal assumes the margin is spread evenly; other methods (power, Shin) can shift heavy favourites and longshots slightly.
Questions
- Is the no-vig price the true probability?
- It is the market's fair price after removing the margin, not a guarantee. It is a useful benchmark to compare your own number against.
- Why does hold matter?
- Higher hold means you need a bigger edge just to break even. Comparing hold across books shows where the price is cheapest.
Related tools
- Odds ConverterConvert American, decimal and fractional odds and see the implied probability.
- EV & Break-EvenExpected value, expected ROI and break-even probability at your own win-probability estimate.
- Build Your Own Fair LineAdd up your own adjustments into your own spread, then compare it with the sportsbook line.
Read the guideHow to Remove the Vig and Find Fair Odds