You open a market and see -110 on both sides. Each price says you need to win about 52.4% of the time to break even. Add them together and you get more than 100%.
The teams have not found a way to win 104.8% of the game. You are seeing the sportsbook's margin built into the prices.
Removing that margin gives you a cleaner view of what the market is saying. It does not tell you who will win. Here is how to do it with a basic calculator—and where the calculation can fool you.
Method and sources checked October 25, 2026, at 8 a.m. EDT. Every price below is a made-up teaching example, not a current sportsbook quote.
1. Start with the whole market
Use all possible outcomes from the same sportsbook at the same time. For a basketball spread with a half-point line, that means both teams at the exact opposite spread. For a player prop at 24.5 points, use over 24.5 and under 24.5.
Over 24.5 at one book and under 25.5 at another are different tickets. Mixing them will not reveal either book's margin. The same problem shows up when one price is from this morning and the other is from five minutes before tipoff.
For a three-way soccer result, include home, draw and away. Leaving out the draw makes the total meaningless. Smarkets' margin guide explains why the implied chances of every outcome need to be added together.
2. Turn each price into a percentage
American odds have two short formulas. Use the size of the negative number, without its minus sign.
- Negative odds: number ÷ (number + 100). At -150, that is 150 ÷ 250 = 60%.
- Positive odds: 100 ÷ (number + 100). At +130, that is 100 ÷ 230 = about 43.48%.
If you use decimal odds, divide 1 by the odds. Decimal 2.00 gives 50%. These are the break-even percentages built into the prices; they are not verified chances of winning. Our guide to reading betting odds walks through that difference.
3. Add the percentages
Take a made-up two-way market priced -150 on Team A and +130 on Team B. Assume there is no draw or push.
| Outcome | Price | Implied chance |
|---|---|---|
| Team A | -150 | 60.00% |
| Team B | +130 | 43.48% |
| Total | Both outcomes | 103.48% |
The total exceeds 100% by about 3.48 percentage points. That extra amount is called the overround. It describes the pricing of this market, not a promise that the book will earn exactly 3.48% of everything wagered. The actual betting mix and results matter.
For -110 on both sides, the total is about 104.76%, an overround of 4.76 percentage points. Keep the full calculator values until the last step so rounding does not creep into your answer.
4. Divide each chance by the total
Now shrink the two implied chances in the same proportion until they add to 100%. This is a simple proportional method of removing the vig:
Example · -150 / +130
Same price story. Margin removed.
Rounded benchmark chances—not measured win probabilities.
Using unrounded inputs, Team A lands at about 57.98% and Team B at 42.02%. Those correspond to roughly -138 and +138 without the margin under this method. Both sides now fit inside one 100% pie.
With -110 on both sides, the same process turns 52.38% and 52.38% into 50% each. The corresponding no-vig price is +100 on either side.
The assumption matters: we removed the margin proportionally. Other methods allocate it differently. This is a transparent benchmark, not a way to discover an objective true chance from two prices.
5. Compare an identical ticket
Suppose another sportsbook offers Team A at -135 while your reference market is still -150/+130. The -135 requires about 57.45% to break even. Your proportional benchmark is about 57.98%.
That small gap is a reason to look closer. It is not proof of a profitable bet. A small change in the underlying estimate, different settlement terms or a stale reference price can wipe it out.
Keep the event, side, line and overtime rules identical. A hockey regulation win and a moneyline including overtime are different outcomes. So are 2+ shots and over 2.5 shots. Our player-prop comparison guide helps keep those details straight.
The part a no-vig calculator cannot do
Removing margin does not fix a badly priced market, predict injuries or tell you whether a player's role has changed. A 58% benchmark can be wrong, and a bet with a good price can still lose.
Pushes need care, too. At an integer total or spread, both bets can refund. Normalizing the two prices gives a comparison conditional on a decisive result; it does not estimate how often a push happens. Start with a half-point market while learning this method.
Exchange commission, promotional payouts and special settlement rules can also change the return. The simple examples above assume ordinary cash bets with no separate fees.
A useful routine is to save both reference prices and their timestamp, do the calculation, then compare the exact ticket you can actually buy. Keep the result in your betting log as a market benchmark. Do not relabel it as your personal prediction.
Once you have placed a supported bet, BetSlip Live can help you import the slip, review its legs and follow live progress. The calculation comes before the ticket; the tracking comes after.