Converting Baseball Betting Odds to Implied Probability

By 4Baseball Staff · November 5, 2026 · 9 min read

How to turn American, decimal and fractional baseball odds into implied probabilities, remove the sportsbook's margin, and see what a price really says. Math and worked examples only, with no picks.

Every betting price is a statement about probability, and the three formats in common use (American, decimal and fractional) are three ways of writing the same idea. A price of -150 on a baseball team tells you that a bettor must risk $150 to win $100, and it also tells you that, ignoring the sportsbook's fee, the market is treating that team as roughly a 60 percent proposition. Learning to move between the two views is the single most useful skill for reading an odds board.

This article explains the conversions with formulas and worked examples, shows how the sportsbook's margin (the vig) is built into the numbers, and demonstrates how to strip it out. It also explains why a probability implied by a price is not a prediction, and how the same arithmetic makes parlays more expensive than they look. It contains no picks and no advice about any game.

Gambling carries risk, and no method of reading a price removes it. Betting is for adults of legal age where it is legal. If gambling is causing you or someone you know problems, the national helpline in the United States is 1-800-GAMBLER, and the National Council on Problem Gambling offers information and support.

Three ways to write one price

American odds use a plus or minus sign and a number. A negative number, such as -150, is the amount you must risk to win $100. A positive number, such as +130, is the amount you win on a $100 bet. A price of +100 or -100 is the same thing and is usually called even money.

Decimal odds give the total return per unit staked, including the stake. A decimal price of 2.50 means that a $1 bet returns $2.50 if it wins, which is $1.50 of profit plus the $1 back. Decimal prices are the standard in much of the world and are the easiest to compute with.

Fractional odds give the profit relative to the stake. A price of 3/2 means $3 of profit for every $2 staked. Fractions are the traditional format in British racing and are the style you will meet most often on British-style sites.

The same price in all three forms looks like this:

Decimal figures are rounded to two places. The fourth column is the implied probability, which the next sections derive.

Converting American odds to a probability

The implied probability of a price is the share of the time a bet must win to break even. For American odds there are two formulas, one for each sign.

For a negative price, divide the number (without the minus sign) by itself plus 100:

Probability = |odds| / (|odds| + 100)

For a positive price, divide 100 by the number plus 100:

Probability = 100 / (odds + 100)

Worked examples:

• -150. The probability is 150 / (150 + 100) = 150 / 250 = 0.60, or 60 percent. If you bet $150 to win $100 and the bet wins 60 percent of the time, you break even: 60 wins of $100 and 40 losses of $150 net to zero per 100 bets of that size.
• +130. The probability is 100 / (130 + 100) = 100 / 230 = 0.4348, or 43.48 percent. A bettor needs to win a little more than 43 times in 100 to break even.
• -110. The probability is 110 / 210 = 0.5238, or 52.38 percent. That is the break-even rate at the standard price for sides, and it is the reason a bettor who wins exactly half of his -110 bets loses money.

The logic is the same in each case: the price tells you what the winning bet earns relative to what the losing bet costs, and the break-even probability follows from that ratio.

Decimal and fractional odds

Decimal odds convert with one step: probability is 1 divided by the decimal price.

Probability = 1 / decimal

A price of 2.50 gives 1 / 2.50 = 0.40, or 40 percent. A price of 1.67 gives 1 / 1.67 = 0.5988, which rounds to 60 percent and matches the American -150 above.

For fractions, with a profit of a for every b staked, the probability is b divided by (a + b):

Probability = b / (a + b)

A price of 3/2 gives 2 / (3 + 2) = 0.40, or 40 percent. A price of 1/2 gives 2 / (1 + 2) = 0.667, or 66.7 percent. A price of 11/10 gives 10 / 21 = 47.6 percent.

To convert between formats, use the decimal figure as the hub. From American to decimal: for a positive price, decimal = 1 + (odds / 100); for a negative price, decimal = 1 + (100 / |odds|). So +130 becomes 1 + 1.30 = 2.30, and -150 becomes 1 + 100/150 = 1.667. From fractional to decimal: decimal = 1 + (a / b), so 3/2 becomes 2.50.

Why the probabilities add to more than 100 percent

A sportsbook offers a price on each side of a game, and the implied probabilities of the two sides should add to 100 percent if the prices were fair. They do not. They add to more, and the excess is the sportsbook's margin, usually called the vig or juice.

Take a baseball moneyline with Team A at -140 and Team B at +120. The implied probabilities are:

• Team A: 140 / 240 = 58.33 percent
• Team B: 100 / 220 = 45.45 percent

Together they come to 103.79 percent. The extra 3.79 points is the overround. A book that takes balanced action on both sides keeps about 3.65 percent of the money wagered (1 minus 1/1.0379). The mechanics are covered in what the vig is and how sportsbooks make money on baseball, and the key idea here is simple: the margin is built into the prices, so every implied probability is slightly inflated.

The common -110 on both sides of a point spread or a total gives a cleaner example. Each side implies 52.38 percent, so the pair adds to 104.76 percent, and the book keeps about 4.55 percent of balanced action. Over many bets, that is the cost a bettor has to overcome before earning any profit.

Removing the vig to find a fair probability

To estimate what the market thinks the true chances are, divide each implied probability by the total, which scales them down so that they sum to 100 percent. This is the simplest method of removing the vig, and it assumes the margin is spread proportionally across both sides.

For the example above:

• Team A: 58.33 / 103.79 = 56.2 percent
• Team B: 45.45 / 103.79 = 43.8 percent

The no-vig prices are therefore about 56.2 percent and 43.8 percent, which convert back to roughly -128 and +128. The sportsbook's actual prices of -140 and +120 are shifted away from those fair values on both sides, and the gap between the real price and the fair price is the cost of making the bet.

Two cautions apply. The method is an approximation, because books do not always spread the margin evenly, and heavy favorites and long shots can carry a larger share of it. And the no-vig figure is the market's estimate, which is not the same as the truth. It is a more honest starting point than the raw implied probability, but it is still a number produced by a market, not a measurement of the teams.

From a probability back to a price

The reverse conversion is useful when you have your own estimate of a probability and want to compare it with a price. For a probability p of 0.50 or more, the American price is negative:

Odds = -100 × p / (1 - p)

For p below 0.50, the price is positive:

Odds = +100 × (1 - p) / p

Examples: p = 0.60 gives -100 × 0.60 / 0.40 = -150. p = 0.40 gives +100 × 0.60 / 0.40 = +150. p = 0.55 gives -100 × 0.55 / 0.45 = -122. For decimal, the price is simply 1 / p, and for a fraction, the profit-to-stake ratio is (1 - p) / p.

What an implied probability does not tell you

A price is not a forecast of a single game. It is a market's collective estimate, shaped by the information available and by how much money the book expects on each side. Baseball makes the gap between estimates and outcomes especially wide, because the sport produces so much randomness in individual games. Even the best teams lose a large share of the time: a team that wins 100 games in a 162-game season has a winning percentage of 61.7 percent, and one that wins 110 wins 67.9 percent. Even a team that loses 100 games wins up to 62 of them.

That compresses the range of moneylines. A team's price in a game depends heavily on who is starting, so the same club can be a favorite in one game and an underdog in the next. The implied probability is a statement about that particular matchup on that particular day, not a rating of the team.

It also means that a single result says almost nothing about whether a price was right. If a team priced at -150 loses, the price was not wrong, because a 60 percent chance loses 40 times in 100. Judging the quality of prices takes hundreds of results, not one.

For the related markets, the run line and totals have their own conventions: the run line and why it is usually 1.5 runs and MLB over/under totals and what moves them explain the structure, and the same conversions apply to every price on those boards.

Break-even rates and expected value

The implied probability of a price is also the break-even rate for a bettor who treats the price as fixed. Expected value, abbreviated EV, turns that into a number: the average profit or loss per bet if a given probability is correct.

The formula for a bet that wins with probability p, pays a profit W and loses a stake S, is:

EV = p × W - (1 - p) × S

Take a $100 bet at -150, which pays $66.67 in profit. If the true probability of winning is 60 percent, EV = 0.60 × 66.67 - 0.40 × 100 = 40.00 - 40.00 = $0. If it is 55 percent, EV = 0.55 × 66.67 - 0.45 × 100 = 36.67 - 45.00 = -$8.33. If it is 62 percent, EV = 0.62 × 66.67 - 0.38 × 100 = 41.33 - 38.00 = +$3.33.

The calculation is only as good as the probability that goes into it. The sportsbook's margin means that, if you accept the market's no-vig probability as correct, every bet has a negative expected value equal to roughly the vig. A bettor who believes he has found an edge is saying that his probability differs from the market's by more than the margin. That is a strong claim, and many bettors overestimate their own edge.

Parlays: how the margin compounds

A parlay combines two or more bets, and every leg must win. The decimal prices multiply. Two legs at -110 each have decimal prices of 1.909, so the parlay pays 1.909 × 1.909 = 3.645, which is about +264 in American odds.

The fair price for two independent 50 percent events is 25 percent, which is +300. The parlay pays +264. If both legs are true coin flips, the expected return per dollar is 0.25 × 3.645 = 0.911, a loss of 8.9 cents per dollar, against 4.5 cents on a single -110 bet (0.5 × 1.909 = 0.955). The loss roughly doubles with two legs and keeps growing with each added leg, which is why parlays are attractive to sportsbooks.

The implied probability of that +264 parlay is 100 / 364 = 27.5 percent, compared with the 25 percent the two legs actually have if each is a coin flip. The difference is the margin, compounded.

Common mistakes in reading prices

• Treating a negative number as a probability. A -150 line is not 150 percent of anything. Use the formula.
• Ignoring the vig. Raw implied probabilities from both sides of a game sum to more than 100 percent. Normalize before comparing with your own estimate.
• Comparing prices across formats without converting. Convert everything to a probability first.
• Reading a result as a verdict. A single outcome cannot tell you whether a price was fair.
• Forgetting that probabilities multiply. Combining legs multiplies both the payouts and the odds against you.
• Assuming a heavy favorite is safe. Even a price of -300 implies a one-in-four chance of losing.

Common questions

What does -110 mean as a probability? 52.38 percent. It is the break-even rate for a bet at that price and includes the sportsbook's margin.

Why does a +100 price imply exactly 50 percent? Because you win as much as you risk, so you need to win half of your bets to break even.

Is a decimal price of 2.00 the same as +100? Yes. Both are even money, and both imply 50 percent before the margin is removed.

How do I remove the vig? Convert both sides to implied probabilities, add them up and divide each by the total.

Does a higher implied probability mean a better bet? No. It means the market thinks the outcome is more likely, and the price you pay for it is already adjusted.

Where to go next

To see how these conversions apply to season-long markets, read season win totals and what they mean and betting on the postseason. Odds boards that you can read with the formulas above are on the odds page. If gambling stops being fun, call 1-800-GAMBLER.