Odds converter: decimal, American, fractional

A single football match can show three different prices for the same outcome: 2.50 on a European soft book, +150 at a US sportsbook, 3/2 at a UK bookmaker. They are identical. If you cannot see that at a glance, you will misread value, miscompare bookmakers, and stake the wrong amount. This is where an odds converter earns its place in a serious bettor's toolkit.

The converter above switches any price between decimal, fractional and American formats, and shows the implied probability behind it. This guide explains what each format means and how to convert by hand when you need to. It also shows how reading the probability behind a price turns a simple format switch into a value check. The goal is not memorising formulas. It is reading any price on any book and knowing instantly what it is really offering you. See how implied probability connects to positive expected value.

Decimal odds are the cleanest. The number is your total return per unit staked, stake included. Odds of 2.50 return 2.50 for every 1 you bet: 1.50 profit plus your 1 back. Decimal is standard across Europe, Australia and most sharp books, and it makes value maths straightforward.

Fractional odds are the traditional UK format, still common in horse racing. The fraction shows profit relative to stake. 3/2 means three profit for every two staked, so a 10 bet returns 15 profit plus your 10 back. Comparison is the awkward part: is 8/5 bigger or smaller than 11/7? You often need decimal to know.

American odds run the US market and centre on 100. A positive number is the profit on a 100 stake, so +150 wins 150. A negative number is the stake needed to win 100, so -150 needs 150 staked to win 100. The flip around even money trips up newcomers constantly.

The converter does this instantly, but knowing the maths means you can sanity-check any tool and never take a wrong number on trust. Decimal is the natural hub: convert everything to decimal first, then out to whatever format you need.

Fractional to decimal

Divide the fraction and add 1. So 3/2 becomes 1.5 + 1 = 2.50. And 5/1 becomes 5 + 1 = 6.00. The plus 1 puts your stake back into the number, which is the whole point of decimal.

American to decimal

For a positive price, divide by 100 and add 1: +150 becomes 1.50 + 1 = 2.50. For a negative price, divide 100 by the number and add 1: -200 becomes (100 / 200) + 1 = 1.50. Once in decimal, the value maths opens up.

Decimal to American

If decimal is 2.00 or higher, subtract 1 and multiply by 100: 2.50 gives (1.50 x 100) = +150. If decimal is below 2.00, divide -100 by the decimal minus 1: 1.50 gives -100 / 0.50 = -200. The 2.00 threshold is the even-money line where American flips sign.

Decimal to fractional

Subtract 1 and express as a fraction. 2.50 becomes 1.5, which is 3/2. Odds of 3.00 become 2, which is 2/1. Non-round results get rounded to standard racing fractions, which is why fractional is imprecise for tight value work.

A worked check: a bookmaker shows -125 on a market. Convert: 100 / 125 = 0.8, plus 1 = 1.80 decimal. That is 4/5 fractional and an implied probability of 55.6%. If your own model says the outcome is closer to 60%, the price is short and there is no value. If your model says 50%, the book is offering more than the true chance, and you may have a positive expected value bet.

Converting between formats is housekeeping. Converting a price into a probability is where the edge lives. Every set of odds carries an implied probability, and comparing that number against your own estimate is the core of value betting.

From decimal, the formula is simple: implied probability equals 1 divided by the decimal odds. So 2.50 gives 1 / 2.50 = 0.40, or 40%. Odds of 1.50 give 1 / 1.50 = 66.7%. The shorter the price, the higher the implied probability, because the book thinks the outcome is more likely.

There is a catch that trips up every beginner. Add up the implied probabilities of all outcomes in a market and the total exceeds 100%. A two-way market priced at 1.91 each side implies 52.4% plus 52.4%, which is 104.8%. That extra 4.8% is the overround, also called the vig or juice: the bookmaker's built-in margin.

Raw implied probability is therefore inflated. To find the book's honest estimate you strip the margin out, a process called devigging. On soft books the margin is heavy, often 5% to 8%, so the raw number overstates the true chance by a wide margin. On a sharp book like Pinnacle the margin runs far lower, which is why sharp prices are treated as the closest thing to true odds. Our no-vig odds calculator does the devig maths for you and returns the fair price.

This is the mechanism behind value betting in one line. Convert a soft book's price to implied probability, then compare it against the devigged sharp probability. If the soft price implies a lower chance than the sharp market's true estimate, you have found value. Our implied odds calculator turns any price into its probability in a click. The formats are just the surface. The probability underneath is the signal.

A converter that only swaps formats is a calculator. Used properly, it is the first step of a value check. Here is how conversion feeds real decisions rather than sitting as a party trick.

Comparing across books that use different formats. You spot 2.05 on a European soft book for a market where a US sportsbook shows +98. Convert +98 to decimal: 1.98. The European price is longer, so if you were going to bet, that is the better line. Line shopping only works when every price is in the same language first.

Reading a sharp reference against a soft price. Pinnacle shows 1.95 on a selection; a soft book offers 2.10. Convert both to implied probability: 51.3% versus 47.6%. After you devig the Pinnacle two-way market, the fair probability might land near 50%. The soft book implying 47.6% is offering more than the true chance, which is the definition of a value bet.

Sizing the stake correctly. Staking methods like the Kelly criterion need decimal odds and a probability as inputs. Convert the price, estimate the edge, and only then size the bet. Guessing the stake off a fractional or American price without converting is how bettors overstake short favourites and wreck a bankroll.

Doing this by hand across fifty markets is not realistic. Catching the moment a soft book prices a selection above its true chance is exactly what a value bet scanner automates. It compares soft prices against sharp references in real time and flags the gaps.

Format confusion is cheap to fix and expensive to ignore. Two quick habits prevent most of it. Always convert everything to decimal before comparing anything. And always take the probability step, not just the format step, because the probability is what tells you whether a price is worth backing.

How do I convert decimal odds to American?

For decimal odds of 2.00 or higher, subtract 1 and multiply by 100: 2.50 becomes +150. For decimal below 2.00, divide -100 by the decimal minus 1: 1.50 becomes -200. The 2.00 mark is even money, where American odds switch between plus and minus. The converter above handles this instantly in both directions.

What does implied probability mean?

Implied probability is the chance of winning that a price suggests, found by dividing 1 by the decimal odds. Odds of 2.50 imply 40%. It is the bookmaker's view of the outcome, but it includes their margin, so the raw figure always overstates the true chance across a full market. Strip the margin to see the fair estimate.

Why do the probabilities in a market add up to more than 100%?

That excess is the overround, or vig: the bookmaker's built-in margin. A two-way market priced 1.91 each side implies 104.8% total. The extra 4.8% is how the book profits over time. To read the honest probability you devig the market, removing the margin. Soft books carry heavier margins than sharp books like Pinnacle.

Which odds format is best for value betting?

Decimal, without much contest. It converts to implied probability in one step, makes comparison across books trivial, and feeds directly into staking formulas. Fractional and American are fine to read, but most value bettors convert everything to decimal before running any value or stake calculation, because the maths is cleaner and less error-prone.

Does an odds converter guarantee I find value?

No. A converter is a reading tool, not a profit tool. It tells you what a price means and what probability it implies, but finding value still requires your own probability estimate or a sharp reference to compare against. Betting carries real risk of loss, and no conversion changes that. The converter simply removes the guesswork from reading the price.

How accurate are converted fractional odds?

Fractional odds are often rounded to standard racing fractions, so the displayed fraction may not match the exact decimal price. For casual reading this is fine. For tight value work on thin edges, convert to decimal and trust that number. The rounding in a fraction can hide or invent small amounts of value that change your decision.

Arthur, Co-founder of ValueBetFactory. Published August 2026, last updated August 2026. Informational content only, not financial advice. Betting involves risk. Past performance does not guarantee future results. Bet responsibly. If you or someone you know has a gambling problem, visit begambleaware.org, GamCare, or in the US the NCPG. You must be of legal age to bet in your jurisdiction, 18+ in most regulated markets, 21+ in many US states.