American odds, decimal odds and implied probability: what the numbers mean
Use it as an American odds calculator when a sportsbook shows plus and minus prices, and as an odds converter when you need decimal odds or the implied probability. Any betting odds calculator takes one price in and gives the others out, and as a betting odds calculator it also gives the payout on any stake. An American odds calculator and an odds converter are the same tool seen from two sides. The same price can be written three ways. American odds are what US sportsbooks show: a negative number is the stake needed to win 100, and a positive number is the profit on a 100 stake. Decimal odds are the total return per 1 staked, stake included, so 2.00 doubles your money. Implied probability is the chance the price assigns to the outcome, equal to 1 divided by the decimal odds. The three always agree, which is why they convert cleanly in both directions.
The same prices in three forms| American | Decimal | Implied probability |
|---|
| -200 | 1.50 | 66.7% |
| -110 | 1.91 | 52.4% |
| +100 | 2.00 | 50.0% |
| +150 | 2.50 | 40.0% |
| +400 | 5.00 | 20.0% |
A price of -110 implies a chance of about 52.4%, not 50%. That small excess is the first sign of the margin, covered below.
Why the two sides add up to more than 100%
If a market were priced without any margin, the implied probabilities of its outcomes would add up to exactly 100%. They do not. A sportsbook shades every price so that the implied probabilities total more than 100%, and the amount over is its margin, called the vig or the juice. On a standard point spread priced at -110 on both sides, each side implies 52.38%, the total is 104.76%, and the margin is 4.76%. That margin is what you pay, on average, for the right to place a bet.
Removing the margin gives the fair probabilities, the chances you would see if the book took no cut. The simplest method divides each implied probability by their total, and it is the one the calculator uses. It assumes the margin is spread across both sides in proportion, which is a reasonable approximation for even markets and a rougher one for heavy favorites and long shots.
Margin removed from three markets| Prices | Margin | Fair probabilities | Fair American odds |
|---|
| -110 / -110 | 4.76% | 50.0% / 50.0% | +100 / +100 |
| -150 / +130 | 3.48% | 58.0% / 42.0% | -138 / +138 |
| -300 / +240 | 4.41% | 71.8% / 28.2% | -255 / +255 |
How to use it
Compare the fair probability with your own view. If you think a team has a 60% chance and the fair price implies 55%, the market undervalues it, and a bet at that price has positive expected value on your estimate. Margins also differ between apps and between markets, so the same game can cost you more at one book than at another. Checking two or three apps before a bet is the easiest way to pay less margin.
These numbers describe prices, not outcomes. A fair price loses as often as it should, and a long run of results can sit far from the average. Treat the calculator as a way to understand what you are paying and not as a promise of profit, and bet only what you can afford to lose.
To see what a welcome offer is worth after play-through, or to price a multi-leg bet, use the bonus value and parlay calculators. For the basics of reading a line, start with the learn section.
The break-even rate: how often you must win
Every price has a break-even win rate, the share of bets you must win to come out even over time. It equals the implied probability, with the margin included. At -110 you stake 110 to win 100, so you need to win 52.38% of your bets to break even. At +150 you need only 40%, because each win pays more. The table gives the break-even rate for common prices.
Break-even win rate by price| American odds | Break-even win rate |
|---|
| -300 | 75.00% |
| -200 | 66.67% |
| -150 | 60.00% |
| -110 | 52.38% |
| -105 | 51.22% |
| +100 | 50.00% |
| +150 | 40.00% |
| +250 | 28.57% |
| +400 | 20.00% |
These are not forecasts. They are the bar a bet must clear. If you believe a side wins more often than its break-even rate, the price is attractive to you, and if you do not have a view, the margin works against you. The gap between -110 and -105 is 1.16 percentage points of win rate on every single bet, which is why comparing prices across apps is worth the minute it takes.
Why parlays cost more
A parlay multiplies the prices of its legs, and the sportsbook's margin multiplies with them. Suppose every leg is a fair 50% chance, priced at -110. Each extra leg lowers the true chance of winning by half, while the price lowers it by less, so the gap between the price and the truth grows with every leg you add.
A parlay of legs priced at -110 each, against a fair 50% chance per leg| Legs | Chance implied by the price | Fair chance | Price above fair |
|---|
| 1 | 52.38% | 50.00% | 4.8% |
| 2 | 27.44% | 25.00% | 9.8% |
| 3 | 14.37% | 12.50% | 15.0% |
| 4 | 7.53% | 6.25% | 20.5% |
| 5 | 3.94% | 3.13% | 26.2% |
A single bet costs about 4.8% above the fair chance. A four-leg parlay costs more than 20%. That does not make a parlay wrong to place, since the payout is larger and many people bet them for fun, but it does mean the same stake costs more on average than a single bet.
Fractional odds, decimal odds and payout
You may meet odds in other forms on other sites. Decimal odds are used in Europe, and fractional odds in the United Kingdom and for horse racing. The three describe the same thing.
The same prices in four forms| American | Decimal | Fractional | Implied probability |
|---|
| -200 | 1.50 | 1/2 | 66.7% |
| -150 | 1.67 | 2/3 | 60.0% |
| +100 | 2.00 | 1/1 (evens) | 50.0% |
| +150 | 2.50 | 3/2 | 40.0% |
| +200 | 3.00 | 2/1 | 33.3% |
| +400 | 5.00 | 4/1 | 20.0% |
Common mistakes when using odds
- Treating the implied probability as the true chance. It includes the margin, so it adds up to more than 100% across a market.
- Removing the margin from a market with more than two outcomes with a two-way method. Use all outcomes together.
- Comparing a price in one format with a price in another by eye. Convert both first.
- Forgetting that the same game can be priced differently at two apps.
- Reading a fair price as a promise. A fair price loses as often as its probability says, and runs of bad results are normal.
A worked margin example
Take a market with Team A at -150 and Team B at +130. The break-even rates are 60.0% for -150 and 43.5% for +130. Together they add up to 103.5%, so the margin is 3.48%. Enter both prices into the margin remover and it divides each rate by the total. The fair chances come out at about 58.0% and 42.0%, and the fair prices at about -138 and +138. Those are the prices the market would show if the sportsbook took no margin.
The fair prices are a reference, not an offer. No app has to show them, and the calculator does not say which side to bet. What they let you do is see how much of a price is margin and how much is the market's view of the game.
Using the result to compare apps
The same game can carry slightly different prices at different apps, and the margin differs with them. Enter each app's two prices into the margin remover one after the other and compare the margin it reports. The lower margin is the cheaper market to bet on, on average. When you want one side, the odds comparison calculator lines up the prices from up to four apps and names the best price for the side you want, so you do not have to compare them by eye.
What the calculator does not do
It converts prices and removes a margin. It does not know which side will win, it does not account for promotions or boosted prices, and it does not read an app's rules for pushes, voids or overtime. A fair price is a reference point for judging the price you are offered, not a promise about the result. Treat every figure as arithmetic on the numbers you typed.
Checking your own arithmetic
It is worth doing one conversion by hand to be sure you understand the tool. Take -150: divide 150 by 250 to get 60%. Take +130: divide 100 by 230 to get 43.5%. Enter both prices and the calculator should agree. When it does not, the most common cause is a typo in the sign, for example +150 typed as 150 with a minus sign missing.
Reading the output
The converter shows three figures for any price: the other format, the implied probability and, where it applies, the payout. Read the implied probability as the bar the bet has to clear. If your own honest estimate of the chance is below it, the price is working against you, and if it is above it, the price is in your favor. Neither tells you the result of a single game.
Frequently asked questions
How do I convert American odds to a percentage?
For a negative price, divide the number without its sign by that number plus 100. For a positive price, divide 100 by the price plus 100. So -150 gives 150 / 250 = 60%, and +150 gives 100 / 250 = 40%.
What is a good margin to see?
Lower is better for you. On a two-way market priced at -110 each way the margin is 4.76%. Prices closer to -105 on both sides carry a smaller margin. Margins are usually higher on props and parlays.
Why does the margin remover only take two prices?
It handles a market with two outcomes, such as the two sides of a spread or an over and under. A market with three outcomes, such as a soccer match with a draw, needs all three prices together.
Does a fair price mean I will win?
No. A fair price means the book takes no margin. It does not change the fact that each bet is uncertain, and long losing runs happen even at fair prices.
Can I use decimal odds here?
Yes. The converter accepts American odds, decimal odds or an implied probability and shows the other two.
