A coin flip should pay even money. Most sportsbooks price a football side at -110 on both teams instead, so you risk $110.00 to win $100.00 whichever team you pick. That gap between -110 and +100 is the vig, and on most lines it is the only thing standing between the posted price and the fair one. A vig calculator takes it back out.
The no vig calculator above works out that gap for any line. Type in every side of a market and it returns the bookmaker’s margin, the fair win probability for each side and the fair American odds. It doubles as a vig calculator for checking how expensive a market is before you bet into it.
How to use the no vig calculator
Enter the prices for every outcome of one market. For a moneyline, spread or total that means two prices; for a soccer match result it means three. Formats can be mixed: the tool turns American, decimal and fractional prices into decimal odds first.
The output starts with the total implied probability and the margin above 100%, usually called the overround. Then come the fair probabilities, which always total exactly 100%, and the fair odds in American format. The hold, the share a sportsbook keeps on balanced action, is not a separate line, but it follows from the total in one step: 1 minus 1 divided by the total.
All sides must come from the same market at the same moment. Mixing a moneyline from one book with the other side from a second book does not produce a fair price; it produces a comparison between two books, which belongs in the arbitrage betting calculator.
Remove the vig: the formula behind it
The method fits in a small table:
| Step | Calculation |
|---|---|
| Implied probability of each side | 1 ÷ decimal odds |
| Total implied probability | sum of all sides |
| Overround | total − 1 |
| Hold | 1 − 1 ÷ total |
| Fair probability of a side | implied probability ÷ total |
| Fair decimal odds | 1 ÷ fair probability |
To remove the vig this way is called the proportional method. Each side keeps its share of the total, so a side that implied 60% of a 103.48% book ends up at 60 ÷ 103.48 = 57.98%.
Fair decimal odds convert back to American the usual way. At 2.00 or above, subtract 1 and multiply by 100. Below 2.00, divide -100 by the decimal odds minus 1.
Worked examples: from the posted line to fair odds
Standard -110 / -110. A decimal price of 1.9091 implies 1 ÷ 1.9091 = 52.38% for each side. The total is 104.76%, an overround of 4.76% and a hold of 1 − 1 ÷ 1.0476 = 4.55%. Divide each side by the total and both land on 50.00%, which is fair odds of +100. Nothing surprising, and a good test that the tool behaves.
A moneyline at -150 / +130. The favorite at -150 (decimal 1.6667) implies 60.00%. The underdog at +130 (decimal 2.30) implies 100 ÷ 230 = 43.48%. Together they reach 103.48%, so the hold is 3.36%.
| Side | Posted | Implied | Fair probability | Fair odds |
|---|---|---|---|---|
| Favorite | -150 | 60.00% | 57.98% | -138 |
| Underdog | +130 | 43.48% | 42.02% | +138 |
The fair line is -138 / +138. Both fair prices are better for the bettor than the posted ones, the favorite moving from -150 to -138 and the underdog from +130 to +138, because the margin was spread across both sides.
A live line at -400 / +300. Late in a game a team leading by two scores might sit at -400, with the trailing team at +300. The implied probabilities are 80.00% and 25.00%, for a total of 105.00%. The overround is 5.00% and the hold is 4.76%, a little more than the pregame -110 market charged. With the vig removed the leader is 76.19% and the trailer 23.81%, which works out to fair odds of -320 and +320.
A three-way soccer line. Home +150, draw +240 and away +190 imply 40.00%, 29.41% and 34.48%. They add up to 103.89%, a hold of 3.75%. The fair probabilities are 38.50%, 28.31% and 33.19%, which in American terms is about +160, +253 and +201.
Using fair odds to judge a price
Fair odds are a yardstick. Once the no vig calculator has produced a fair price, any offer longer than that price has positive expected value by the market’s own estimate, and any offer shorter has negative expected value.
Take the underdog from the second example, fair at +138 with a 42.02% fair probability. If a second sportsbook offers that same underdog at +150 (decimal 2.50), the expected return per dollar is 0.4202 × 2.50 − 1 = 0.0504, roughly 5 cents per dollar staked. If it offers +125 (decimal 2.25), the figure is 0.4202 × 2.25 − 1 = −0.0546, about 5.5 cents lost per dollar.
That is the basic use of a fair odds calculator: it converts a vague sense that a price looks generous into a number. The yardstick is only as good as the market it came from, though. A sharp, high-volume market produces a fair price worth trusting. A thin in-play prop with a wide margin produces a fair price that is little more than the book’s guess with the margin peeled off.
Professional bettors often go a step further and compare their bet with the fair price at the close of the market. That idea, and why it predicts long-run results better than a single win or loss, is covered in the closing line value guide.
Vig in live betting: why in-play lines cost more
In-play markets usually charge a wider margin than the same game before kickoff. The reasons are structural. Prices are set by models reacting to every play, the book cannot wait for sharp money to correct a mistake, and bet delay plus market suspensions limit how often the line can be traded. The book prices that uncertainty into the line.
The numbers show it. The -110 / -110 pregame line carries a 4.55% hold; the -400 / +300 live line in the example carries 4.76%. On live props and alternate lines the total implied probability can climb much higher. A live player prop at -140 / +105 adds up to 58.33% + 48.78% = 107.11%, a hold of 6.64%, which means a bettor needs a real edge just to break even.
Running a line through the vig calculator before you bet is the quickest way to know which in-play markets are cheap and which are expensive. A wide margin is not a reason on its own to avoid a bet, but it raises the bar your opinion has to clear.
A no vig calculator on spreads, totals and props
Spreads and totals work the same way as moneylines, with one condition: both prices must be on the same number. Over 47.5 at -105 and Under 47.5 at -115 imply 51.22% and 53.49%, a total of 104.71%. With the margin removed the Over is 48.92% and the Under 51.08%, roughly +104 and -104. The market leans slightly to the Under, and the posted prices hid that lean inside the vig.
Alternate lines need more care. A book that offers Over 50.5 at +140 and Under 50.5 at -175 is pricing a different question, and the fair odds calculator only answers it for 50.5. Do not combine an alternate Over with the main Under.
Player props are where the tool earns its keep. Many props are posted at -115 / -115 or wider, and some only show one side, such as “anytime touchdown” at +180 with no “no” price at all. A one-sided prop cannot be stripped of its vig, because there is no second price to measure the margin against. Treat the implied probability (here 35.71%) as an upper bound on what the market thinks, not as a fair estimate. When both sides are listed, run them through the no vig calculator before comparing them with a prop at another book, since props are where margins vary most from one sportsbook to the next.
When the simple method is not enough
The proportional method treats every side the same way. That is a reasonable default for close lines, and it is what the calculator uses.
On lopsided lines there is a known complication. Bettors overpay for longshots, a pattern usually called the favorite-longshot bias, and sportsbooks tend to load more of their margin onto the longshot side. A proportional split then makes the longshot look slightly more likely than the market really thinks. Other approaches exist, including additive, power and Shin adjustments, and each moves the margin toward the longshot by a different amount. On a -110 / -110 line they all agree. On a -1000 / +600 line they can differ by a few tenths of a percentage point.
A second limit is the market itself. Removing the vig assumes the posted line already reflects the true chances once the margin is gone. A line that is stale because it has not caught up with an injury, or a live line that has been suspended for twenty seconds while the ball is in the air, does not become accurate just because the margin has been stripped out.
A third limit catches people with spreads. The fair probabilities apply to that exact number. A -3.5 spread priced at -110 / -110 says the market sees the favorite covering 3.5 points as a coin flip, not that it sees the game as even.
One last practical point. When one side of a market is suspended and only the other shows a price, there is nothing to divide by. The calculator needs both prices from the same moment, so a live market caught halfway through repricing will return a fair price for a line that no longer exists.