Free tool
Odds Converter
Switch between decimal, fractional and American odds instantly, and see the implied probability behind any price.
3.50 = 5/2 = +250 = 28.6% implied
| Decimal | Fractional | American | Implied |
|---|
Type into any box and the others update. Fractional odds are shown to the nearest common bookmaker price; the decimal figure is exact.
How odds formats work
Decimal odds show your total return per £1 staked, including the stake. Odds of 3.50 return £3.50 for every £1. Exchanges and most European bookmakers use decimals, and every calculator on this site does too.
Fractional odds show profit relative to stake. 5/2 means £5 profit for every £2 staked, so a £10 bet returns £25 profit plus your £10 back. They are still the default on UK high-street bookmaker sites.
American odds use a baseline of 100. A positive number (+250) is the profit on a £100 stake; a negative number (−150) is the stake needed to win £100.
Implied probability
Divide 1 by the decimal odds to get the probability the bookmaker is pricing in. Odds of 3.50 imply a 28.6% chance. Add up the implied probabilities of every outcome in a market and you will get more than 100%; the excess is the bookmaker’s margin. When the total is under 100% across different bookmakers, you have found an arb, which is exactly what our arbitrage calculator checks for.
Why matched bettors care
The Oddsmatcher rating on any service is simply the bookmaker’s decimal price divided by the exchange’s decimal price, adjusted for commission. Being fluent in decimals lets you sanity-check a match in your head before you commit a stake.
How do decimal odds work?
A decimal price is the total return on a winning £1 stake, your stake included. Odds of 3.00 return £3 on a £1 bet: £2 profit plus your £1 back. Odds of 1.50 return £1.50: 50p profit plus your stake.
That single difference is why decimal is the format used for matched betting. Fractional odds tell you the profit and make you add the stake back yourself; decimal odds are already the number you need, so the arithmetic in a lay stake calculation works directly. Every exchange prices in decimal for the same reason.
Two shortcuts worth memorising. 2.00 is evens — double your money, a 50% implied chance. Anything below 2.00 is odds-on, anything above is odds-against. And 1 divided by the decimal price is the implied probability, so 4.00 is a 25% chance and 1.25 is an 80% chance.
Common odds conversions at a glance
The converter above handles any price. This table covers the ones that come up most often on a UK board, if you just want to look one up.
| Fractional | Decimal | American | Implied probability |
|---|---|---|---|
| 1/4 | 1.25 | −400 | 80.0% |
| 1/2 | 1.50 | −200 | 66.7% |
| 4/7 | 1.57 | −175 | 63.6% |
| 4/6 | 1.67 | −150 | 60.0% |
| 8/11 | 1.73 | −138 | 57.9% |
| 5/6 | 1.83 | −120 | 54.5% |
| Evens (1/1) | 2.00 | +100 | 50.0% |
| 6/4 | 2.50 | +150 | 40.0% |
| 7/4 | 2.75 | +175 | 36.4% |
| 2/1 | 3.00 | +200 | 33.3% |
| 9/4 | 3.25 | +225 | 30.8% |
| 5/2 | 3.50 | +250 | 28.6% |
| 3/1 | 4.00 | +300 | 25.0% |
| 7/2 | 4.50 | +350 | 22.2% |
| 4/1 | 5.00 | +400 | 20.0% |
| 9/2 | 5.50 | +450 | 18.2% |
| 5/1 | 6.00 | +500 | 16.7% |
| 6/1 | 7.00 | +600 | 14.3% |
| 8/1 | 9.00 | +800 | 11.1% |
| 17/2 | 9.50 | +850 | 10.5% |
| 9/1 | 10.00 | +900 | 10.0% |
| 10/1 | 11.00 | +1000 | 9.1% |
| 12/1 | 13.00 | +1200 | 7.7% |
| 16/1 | 17.00 | +1600 | 5.9% |
| 20/1 | 21.00 | +2000 | 4.8% |
| 25/1 | 26.00 | +2500 | 3.8% |
| 33/1 | 34.00 | +3300 | 2.9% |
| 50/1 | 51.00 | +5000 | 2.0% |
| 100/1 | 101.00 | +10000 | 1.0% |
Implied probability here is the raw price with no margin stripped out. Add up every runner in a real market and the total comes to more than 100% — that excess is the bookmaker’s cut.
Converting decimal odds back to fractions
Going the other way is one step: subtract 1 from the decimal price, then express what is left as a fraction. Decimal 3.50 becomes 2.5, which is 5/2. Decimal 1.80 becomes 0.8, which is 4/5.
The awkward part is that bookmakers round to a traditional fractional ladder rather than showing the exact fraction. A decimal price of 2.76 is not displayed as 44/25; it is shown as 7/4, which is 2.75. That rounding is usually in the bookmaker’s favour by a fraction of a percent, and it is one small reason to work in decimal wherever you can.
Frequently asked questions
Which format should I use?
Decimal, for anything involving a calculation. Most UK bookmakers let you switch the display format in your account settings, and doing that once removes a whole category of mistake. Fractional is fine for reading a board; it is a poor format for arithmetic.
Why do the implied probabilities add up to more than 100%?
That is the bookmaker’s margin, sometimes called the overround. A fair two-way market would price both sides at 2.00 for a total of 100%; a real one might price them at 1.90 and 1.90, which totals about 105%. The 5% is the built-in edge, and it is why matched betting works from promotions rather than from picking winners.
What do American odds mean?
A positive number is the profit on a 100 stake, so +250 wins 250 from 100. A negative number is the stake needed to win 100, so −150 means staking 150 to win 100. They are rarely useful in the UK, but they turn up on US sportsbooks and in odds feeds.
Do exchanges use the same odds as bookmakers?
Same format, different number. Exchange prices are set by users rather than by a bookmaker adding margin, so the lay price you need is usually a little higher than the bookmaker’s back price. The gap between the two is what creates your qualifying loss.
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