Every betting price is a probability in disguise. Convert it, and you can read what the sportsbook thinks a bet's chance really is — but only after you strip out the margin. Here is the conversion in both directions, and the arithmetic that removes the vig from a two-sided market.
A betting line is not really a number — it is a probability wearing a costume. Learn to read the probability underneath, and two things happen. You can compare prices across markets and books on a common scale, and you can see how much of the price is genuine estimate and how much is the sportsbook's cut. Both start with one conversion.
Price to implied probability
American odds come in two flavors, so there are two formulas. Negative odds (favorites) tell you how much you risk to win 100; positive odds (underdogs) tell you how much you win on a 100 risk.
Why both sides sum past 100%
Take a standard two-way market, -110 on each side. Convert both and add them: 52.38% + 52.38% = 104.76%. The two outcomes are exhaustive — one of them must happen — so a fair market would sum to exactly 100%. The extra 4.76% is the overround, the margin the sportsbook has folded into the two prices. It is the reason the raw implied probability always overstates the true chance.
Removing the vig
To find what the market really thinks, strip the margin back out. The standard method rescales both implied probabilities so they sum to 100% again — divide each by the total. On a symmetric -110/-110 market the answer is unsurprising: both sides fall to exactly 50%. The interesting case is a lopsided market, where removing the vig tells you something you could not read off the raw price.
That no-vig probability is the number that matters. It is the market's best estimate with the house cut removed, and it is what you should compare your own estimate against. If you think the favorite is a 68% shot and the no-vig market says 64.3%, you may have found value; if you think it is 64% and the market says 64.3%, you are looking at a fair price with no edge — betting it just pays the vig.
Putting it to work
- Compare on a common scale. Two books quoting -195 and -205 look similar; converting both to no-vig probability tells you which is actually offering the better price.
- Judge your own reads. The no-vig market probability is a disciplined baseline. Beating it consistently is the definition of an edge; failing to beat it means you are paying to play.
- Spot the margin. The gap between a raw implied probability and its no-vig version is exactly the margin you are being charged on that side.
- Watch the method's limits. Simple proportional de-vigging slightly overstates the favorite's fair chance on very lopsided markets; more advanced methods exist, but proportional rescaling is close enough for reading a board.
What this does not do
- It does not produce your win rate. The no-vig number is the market's estimate, not a guarantee and not your own edge.
- It does not beat the book by itself. Removing the vig tells you the fair price; you still need a better estimate than the market to profit.
- It is not a pick. This is a method for reading prices, not a recommendation on any bet.
Frequently asked
How do I convert American odds to a probability?
For a negative price, divide the odds (dropping the minus sign) by that number plus 100: -110 becomes 110/210 = 52.38%. For a positive price, divide 100 by the odds plus 100: +150 becomes 100/250 = 40%. In decimals it is even simpler — the implied probability is one divided by the decimal.
What does 'removing the vig' mean?
Both sides of a market include the sportsbook's margin, so their implied probabilities sum to more than 100%. Removing the vig rescales both sides to sum back to 100% by dividing each by the total. The result is the no-vig, or fair, probability — the market's estimate with the house cut stripped out.
Why is the no-vig probability lower than the raw implied one?
Because the raw implied probability includes margin. On a -200 favorite the raw figure is 66.67%, but once you rescale a 103.70% market back to 100%, the fair chance is about 64.29%. The difference is exactly the margin folded into that side of the price.
Does removing the vig tell me whether to bet?
Only in part. It gives you the market's fair estimate, which is the correct thing to compare your own opinion against. You still have to have a better estimate than the market to have an edge — the no-vig price sets the bar, it does not clear it for you.