Odds Converter

Convert between decimal, fractional and American odds, and see the implied probability.

This converts a price between formats and shows the rate that price breaks even at. It does not tell you the chance of an outcome, because a bookmaker's margin is inside every price it publishes.

One price, four ways. Type in any of them.

Decimal

Total return for each 1 staked.

Fractional

Profit, over the stake that wins it.

American

Plus: profit on a 100 stake. Minus: stake to win 100.

Implied %

100 divided by the decimal price.

What this price means

40.00%

break-even win rate

A 2.50 price returns 2.50× your total stake when it lands, so backing it breaks even if the outcome happens 40.00% of the time. Any less often than that and it loses money over the long run.

The book’s margin is still inside that figure

This price: 2.50 +150implies 40.00%
Other side, at zero margin: 1.67 -150implies 60.00%

This price40.00%Other side60.00%Together100%

Two prices whose implied percentages come to exactly 100% are a market with no margin in it. A real book prices the other side shorter than 1.67, so its two percentages come to more than 100%, and that excess is its cut. The cut is inside this price too, which is why the chance the book actually expects here is lower than 40.00%.

Take the margin out with both prices or check a price against your own estimate in the EV calculator.

What a fractional board could print

US racing board

3/2

2.50 is a rung, so this board could chalk this price exactly. It is written the same way this converter prints it.

UK or Irish book

6/4

2.50 is a rung, so this board could chalk this price exactly. The board writes it 6/4; the converter prints 3/2. Two conventions, one price.

Both boards carry this exact price and write it differently: 3/2 on a US racing board, 6/4 on a UK or Irish book.

The fraction above stays 3/2, the closest simple fraction to the price you entered. Moving a price onto a rung would change the price, which is the one thing a converter should never do quietly.

Every field is rounded for display: decimal and implied probability to two places, American to a whole number. The fraction is the closest simple one to the price, not a rung on the ladder a fractional board prices from, so it often will not match one. The panel above shows the rungs it falls between, and there is no single ladder: a US racing board and a UK or Irish book carry different ones.

Conversion quiz

Best 0

15 rapid conversions, pick the right value before the timer runs out.

Written and reviewed by Alexander Korsager · last reviewed September 26, 2026 · corrections

The idea

Odds are three ways of saying the same thing. Decimal (2.50) is the total return per unit staked. Fractional (3/2) is the profit relative to the stake. American, or moneyline (+150), is the profit on a 100 stake for underdogs, or the stake needed to win 100 for favorites.

Type a price in any format and the others update, along with the implied probability.Read that figure carefully: it is the rate at which backing the price breaks even, not the chance of the outcome. The bookmaker's margin is still inside it, so the chance the book itself expects is lower.
The converter shows you how much lower, without needing a second price.For any price it prints what the other side of a two-way market would have to be for the two implied percentages to add up to exactly 100%. A real book prices that other side shorter, the total comes to more than 100%, and the excess is its margin. Comparing a price against your own estimate is the first step in finding value, and taking the margin out first is what makes the comparison honest.

FAQ

Questions players ask

How do you convert decimal odds to implied probability?

Divide 1 by the decimal odds and multiply by 100. For example, 2.50 decimal odds is 1 / 2.50 = 0.40, or a 40% implied probability.

What do +150 and -200 American odds mean?

A positive number is the profit on a 100 stake: +150 returns 150 profit plus your 100 back. A negative number is the stake needed to win 100: -200 means risking 200 to win 100.

Are these conversions exact?

The formulas are exact in every direction. What you see is rounded: decimal and implied probability to two places, American to a whole number the way books quote it, and fractional to the closest simple fraction. Across prices from 1.10 to 5.00 the worst any of them is out by is about 0.005 in decimal terms, half a cent per dollar returned. All four fields are computed from one underlying price rather than from each other, so they never disagree.

Why does the fraction here not match a bookmaker's board?

Because a fractional board does not price in arbitrary fractions. It prices off a fixed ladder, and the ladder is short: at a UK or Irish book the span above evens runs 11/8, 6/4, 13/8, 7/4, 15/8, 2/1, 9/4, 5/2, 11/4, 3/1. Consecutive rungs across that span are 4.3% to 8.3% apart in return, so most decimal prices fall between two of them and have no fraction of their own. Decimal 2.55 is one. The rungs either side are 6/4 at 2.50 and 13/8 at 2.625, and on a 100 stake those return 250 and 262.50. This converter prints 31/20, which is the closest simple fraction to the price you actually entered, not a price a shop could chalk up. The panel under the tool shows the rungs your price falls between, on either board.

Is there one standard ladder, or does it depend where you bet?

It depends where you bet, and the difference is bigger than it looks. A US racing board works in fifths at short prices and halves above 2/1: 6/5, 7/5, 3/2, 8/5, 9/5, 2/1, 5/2, 3/1, 7/2. A UK or Irish book works in eighths through that same span: 11/8, 6/4, 13/8, 7/4, 15/8, 2/1, 9/4, 5/2, 11/4. The US board has no eighths and the UK one has no 7/5, 8/5 or 9/5, so each is missing prices the other quotes routinely, and the prices they share are not always written the same way: 2.50 is 3/2 at a US track and 6/4 at a UK book. The standard -110 American football price is 10/11, a rung at a UK book and no rung at all on a tote board, which runs 4/5 straight to evens. The panel under the converter is set to the US board by default and switches to the UK and Irish one.

Why do -110 and 1.91 give me two different fractions?

Because 1.91 is not quite -110. That price is 1.909090 and onwards, which is exactly 10/11, and the decimal field rounds it to 1.91 to display it. Enter the American price and the fraction reads 10/11, the one a book would print. Enter 1.91 and the conversion starts again from the rounded number, and the closest simple fraction to it is 91/100. Nothing is broken in either case, and it is the clearest illustration on this page of why a rounded price is not the price.

Is the implied probability the real chance of the outcome?

No, and this is the one thing worth knowing about it. Implied probability is 1 divided by the decimal price, which is the rate at which backing that price breaks even. Every bookmaker prices a market so the implied percentages across all outcomes add up to more than 100%, and that excess is its margin. Because the margin is inside every price in the market, the chance the book actually expects for any single outcome is lower than the implied figure this tool prints.

How much lower than the implied probability is the real chance?

It depends on the market's margin, which you cannot see from one price on its own. What you can see from one price is the reference point: for a two-way market to carry no margin at all, the other side would have to be priced at d / (d − 1), where d is the decimal price you entered. A price of 2.50 implies 40%, so the zero-margin other side is 1.67, implying 60%. Whatever the other side is actually priced at will be shorter than 1.67, and the gap is the margin. To split that margin between the two outcomes and get fair prices, use the no-vig calculator with both prices.

Methodology

How this is calculated

Four ways of writing one number, converted through decimal odds as the common form. Implied probability is p = 1 / d. American odds are (d − 1) · 100 for a price of 2.00 or longer, and −100 / (d − 1) for anything shorter. Fractional odds are the closest simple fraction to d − 1 with a denominator of 100 or less.

That last one is a conversion of the price, not a copy of a bookmaker's board: a fractional board prices off a short fixed ladder, and this tool deliberately shows a finer fraction than the ladder carries, because rounding a price onto the nearest rung would change the price.

The board ladders are shown separately, under the converter, as the rungs a price falls between and what the step between them is worth in return. They are transcribed lists rather than derived ones, and a rung is listed only where two independent published tables for that market carry it.

The zero-margin opposite price is d / (d − 1), the unique second price that makes the two implied percentages sum to exactly 1.

Common misreadings5

The implied percentage is not the probability of the outcome. It is the break-even rate for that price, and the book's margin is inside it, so the chance the book expects is lower.
A price being longer at one book than another does not make it good value. It makes it better value than the other book, which is a different claim and only useful if one of the two is priced sharply.
The zero-margin opposite price is a reference point, not a price anyone is offering. Finding a real market priced at both sides of it would be an arbitrage, and those are rare and short-lived.
Reading the panel against the wrong market is the way to get a wrong answer out of it. The rungs it names are the ones that board carries, and the boards differ: 10/11 is an ordinary UK price and is not a rung a tote board can show, and 13/8 is an ordinary UK price a US track will never display. Switch it to the board you are actually looking at before comparing anything.
The fraction here not matching a board is not the board being wrong, and it is not a rounding detail either. Two adjacent rungs are further apart than they look: 6/4 and 13/8 sit next to each other on the UK and Irish ladder and are 5% apart in return, which is wider than the edge a sharp market realistically leaves in a price. Reading a fraction and a decimal as the same price because they are close is the mistake this costs money on, and it does not become an edge in the other direction: a wider price at a soft book is still a soft book's price.

Assumptions3

The price entered is a back price at a single outcome, staked level, with the stake returned on a win. That is what makes 1 / d the break-even rate.
The zero-margin opposite price assumes a two-way market with exactly two outcomes. A three-way market (1X2, for example) has a third price sharing the total, so its zero-margin pairing is not defined by one price alone.
The break-even rate ignores commission. On an exchange, a commission on winnings raises the rate a back bet actually needs.

Limits6

One price cannot tell you the size of a market's margin, only that there is one. Measuring it needs every price in the market.
Every field is rounded for display and none of them is exact to the price underneath. Decimal and implied probability go to two places, American to a whole number, fractional to the closest simple fraction with a denominator of 100 or less. Across prices from 1.10 to 5.00 the worst any of them is out by is about 0.005 in decimal terms.
The fields never disagree with each other, because all four are derived from one underlying price rather than from one another. Re-typing a value the page displayed is the case where that stops holding: the conversion starts again from the rounded number rather than the one it came from.
The fraction shown is not a price a fractional bookmaker would display. A board prices off a fixed ladder whose rungs run 4.3% to 8.3% apart in return across the UK and Irish 11/8 to 3/1 span, so most decimal prices have no fraction on the board at all, and this tool prints the closest simple fraction to the real price instead of moving the price to fit the ladder.
The two ladders are the rungs two published tables agree on, which is narrower than what every individual book quotes. A UK book will price 4/11, 2/7 or 3/10 at the odds-on end, and one of the two tables lists them while the other does not, so they are not shown here. A price the panel calls off-ladder may still be one a particular book chalks, and the panel says which ladder it is reading against for that reason.
Neither ladder is extended past the range its sources cover: the US board list runs 1/9 to 16/1 and the UK and Irish one 1/5 to 100/1. Real boards show prices outside both, and for those the panel says the price is off the end rather than naming a rung nothing published supports.

Evidence

The conversion formulas are the standard identities between decimal, fractional and American odds, and the zero-margin opposite follows from setting 1/d1 + 1/d2 = 1.

Both are covered in lib.test.ts, which checks that every format round-trips through decimal and that the opposite price this tool prints always makes the two implied percentages sum to 1. A passing test means the code matches the arithmetic, not that any given book's price is fair.

The two board ladders are not ours and are not derived here. They are transcribed, and a rung is listed only where two independent published tables for that market carry it.

The US racing board comes from AmWager's odds and $2 payoff chart and from the same chart in Richard Eng's "Betting on Horse Racing For Dummies", which print identical lists from 1/9 to 16/1; ladders.test.ts re-derives every one of those payoffs from the rung, so a mistyped fraction fails the test rather than reaching the page.

The UK and Irish ladder comes from the conversion tables published by AceOdds and MyBettingSites, checked against their decimal columns, with StableBet's odds guide ("bookmakers don't offer random odds, they work from a standard ladder") corroborating the 11/8 to 3/1 span and GamblingCalc's decimal-to-fractional converter stating the same principle.

Two sources rather than one is deliberate: a third chart consulted for this work prints 9-2 as a $10.50 payoff, which is 2 x 5.25 and not 2 x 5.50, and one published table is not evidence. All sources retrieved 2026-09-10. The rung spacings quoted above are arithmetic on those lists, not a claim about any one board.

Gambling can cause serious harm. The National Problem Gambling Helpline is free, confidential and open 24/7, call or text 1-800-MY-RESET (1-800-697-3738), or chat at ncpgambling.org/chat.

Read up

Go deeper

Related tools