A price of -135 on a screen in Ohio, 1.74 on a European site and 20/27 in fractional form are the same bet. Each one says a $135 stake wins $100, and each one implies a 57.45% chance. They only look different because three betting traditions settled on three ways to write it.
The odds converter above translates between them. Type a price in any of the three formats and it returns the other two, plus the implied probability. That matters most when a price arrives in an unfamiliar format, or when a formula needs decimal odds and the screen shows American ones.
How to use the odds converter
There is one input. Type +150, -150, 2.50, 1.6667, 3/2 or 3:2, and the tool works out which format it is. A sign, or an unsigned number of 100 or above, means American. A slash or colon means fractional. Anything else above 1 is read as decimal.
The four outputs appear together: American, decimal, fractional and implied probability. Decimal odds are shown to three places for prices under 10, enough to tell 1.909 from 1.91. The fractional result is the closest fraction whose bottom number is 100 or less, so a messy price still gets a readable fraction.
The conversion formulas
Every conversion goes through decimal odds, because decimal is the one format that is just a number. The rest of the rules hang off it.
| From | To decimal | From decimal |
|---|---|---|
| American, positive (+A) | 1 + A ÷ 100 | (D − 1) × 100, when D ≥ 2.00 |
| American, negative (−A) | 1 + 100 ÷ A | −100 ÷ (D − 1), when D < 2.00 |
| Fractional (a/b) | a ÷ b + 1 | D − 1, written as a fraction |
| Implied probability (p) | 1 ÷ p | 1 ÷ D |
The split at 2.00 is the only part that trips people up. A decimal price of 2.00 is even money. Above it, the American price is positive and says how much $100 wins. Below it, the American price is negative and says how much must be staked to win $100.
Worked conversions at common prices
One full example first. Take a decimal price of 1.80. It is below 2.00, so the American price is −100 ÷ (1.80 − 1) = −100 ÷ 0.80 = -125. The fractional price is 1.80 − 1 = 0.80, which is 4/5. The implied probability is 1 ÷ 1.80 = 55.56%.
The table below runs the same steps for the prices seen most often.
| American | Decimal | Fractional | Implied |
|---|---|---|---|
| -150 | 1.6667 | 2/3 | 60.00% |
| -135 | 1.7407 | 20/27 | 57.45% |
| -125 | 1.8000 | 4/5 | 55.56% |
| -110 | 1.9091 | 10/11 | 52.38% |
| +100 | 2.0000 | 1/1 | 50.00% |
| +138 | 2.3750 | 11/8 | 42.11% |
| +150 | 2.5000 | 3/2 | 40.00% |
| +250 | 3.5000 | 5/2 | 28.57% |
Two rows deserve a note. The 11/8 row is exactly +137.5, which the converter rounds to +138 because American prices are whole numbers. The -135 row produces 20/27, a correct fraction that few people would ever write by hand.
Why fractional odds look strange after conversion
Fractional odds come from a tradition where prices moved along a fixed ladder of familiar fractions. Boards printed steps such as 4/6, 10/11, evens, 11/10 and 6/4, and the gaps between them were uneven. A decimal or American price that falls between two rungs has no tidy fractional twin.
The converter’s answer is to find the closest fraction it can with a bottom number of 100 or less. For -135 that is 20/27, which is exact. For a price like 1.73 it is 73/100, also exact but clumsy. Neither is wrong; both describe the same payout as the decimal price.
There is a small trap in the other direction. A fraction on a traditional board may itself be a rounded version of the bookmaker’s real price, so converting 8/13 to decimal gives 1.6154, which may not be the exact figure the price was set from. For anything that needs precision, decimal odds are the safer source.
Which format suits which job
Each format grew up in a different place and does one thing well. American odds are the US standard, built around $100: they answer “how much do I win on $100” or “how much do I risk to win $100” at a glance. Decimal odds are the norm across much of Europe, Canada and Australia, and they show the total return per unit staked, which is why every formula on this site runs on them. Fractional odds are the traditional format in Britain and Ireland and show profit relative to stake, so 5/2 reads as “win 5 for every 2 risked”.
None of them is more accurate than the others. They differ in what they make easy. American odds make the size of a win easy to see. Decimal odds make multiplication easy, so a parlay or a hedge is simple arithmetic. Fractional odds make a stake-to-profit ratio easy to say out loud.
A whole market converts the same way, one price at a time. A soccer match at home +150, draw +240 and away +190 becomes 2.50, 3.40 and 2.90 in decimal, and 40.00%, 29.41% and 34.48% in implied terms. The three percentages add up to 103.89%, and that extra 3.89% above 100% is the price of the bet built into the line. If you convert both or all sides of a market before comparing it with another one, the cheaper market is the one whose total sits closer to 100%.
Converting odds during a live game
In-play markets tend to reprice after every play, and many sportsbooks show only one format by default. Converting on the fly is useful for three jobs.
The first is comparison. A live total at -125 on one screen and 1.83 elsewhere are not the same: 1.83 is about -120 in American odds, so the second price pays a little more.
The second is arithmetic. Every serious betting formula, from hedging to parlays to arbitrage, multiplies or divides decimal odds. A live hedge at +185 has to become 2.85 before the stake can be worked out, and doing that in your head while the market is open invites mistakes you would never make at a desk.
The third is probability. A live win-probability figure on a broadcast and a live moneyline are hard to compare until the price is turned into an implied percentage. A team shown at 62% to win and priced at -150 (60.00% implied) is close to fair with the margin still included. The implied probability calculator goes further into that comparison, and the line movement guide explains why live prices jump.
American odds also distort the size of a move. A shift from -105 to +105 looks like 210 points, but in implied terms it is 51.22% to 48.78%, under two and a half points. A shift from -400 to -300 looks smaller, yet it moves the implied chance from 80.00% to 75.00%, a full five points. Converting to percentages before judging a move avoids reading the American numbers as if they were linear.
A side-track: the formats this tool does not read
Three more formats exist, mostly in Asian markets. Hong Kong odds show only the profit per unit, so they equal decimal odds minus 1: 1.50 in Hong Kong odds is 2.50 in decimal. Malaysian and Indonesian odds use positive and negative signs in ways that resemble American odds on a different scale.
The converter does not read them, because US sportsbooks display American odds by default and the Asian formats rarely appear on them. The Hong Kong format is the easy one to handle by hand: add 1, then convert the result as a decimal price.
Pitfalls when converting prices
Rounding is the usual source of small errors. Many sites show -110 as 1.91, which pays $91.00 on a $100 stake, against $90.91 at the exact 1.9091. Over a single bet the gap is nine cents; inside a hedge or an arbitrage split it can tilt the result.
Sign mistakes are the next, and they are costly ones. Reading -150 as +150 turns a bet that wins $66.67 on $100 into one that seems to win $150.00. A price of 150 without a sign is read as +150, because there is no decimal price that large in normal markets. A price of -50 cannot exist in American odds at all, and the tool rejects it.
Implied probability carries the vig. Converting -110 gives 52.38% for each side of a standard line, 104.76% in total. That is not a fair estimate of the chance; it is the break-even rate at that price. Removing the margin takes both sides of the market, which is the job of the no vig calculator.
Fair prices create their own rounding issue. A fair probability of 42.02% converts to +137.98, which displays as +138, and a probability of 57.98% becomes -138. Converting +138 back gives 42.02% again, so nothing is lost on a round trip at this precision. With wider rounding, such as prices shown only in steps of five, a round trip can shift the implied figure by a few tenths of a point, enough to matter when you are checking a thin edge.
Finally, a converted price is only as fresh as the input. A live price copied while the market was suspended may already be gone, and converting a stale +185 into 2.85 produces an exact answer to a question the sportsbook is no longer asking.