Three calculators that do the arithmetic every bet needs, and nothing you have to sign up for. Convert a price between decimal, fractional and American, work out whether a bet actually has value, and see what an accumulator really pays.
They run in your browser, nothing is stored, and every amount is in euros. If you only take one thing from this page, take the implied probability number. It is the shortest route to understanding what a price is really telling you.
Reviewed byFred AndersonPick a tab. Every field updates as you type, so you can work backwards from a probability just as easily as forwards from a price.
Type into any field and the others follow. Returns are shown in euros.
Compare the price on offer with your own read of the chance. Anything above zero edge is a bet worth making.
Add each selection and see the combined price, the return and what the bookmaker margin does across the legs.
The same price gets written three different ways depending on where the bookmaker grew up. None of them is better than the others, they just count from different starting points.
A price of 2.50 means a winning bet returns two and a half times the stake, your money back included. Ten euros back at 2.50 is 25 euros in the account, of which 15 is profit. This is the standard across mainland Europe and it is the easiest to do sums with, which is why every calculator on this page works in decimal underneath.
Written 3/2, said as three to two, it tells you the profit rather than the return. Stake two, win three, get five back. Common in the UK and Ireland and on horse racing everywhere. The trap is that 3/2 and 2.50 are the same price, and the fraction never includes your stake.
A plus number is the profit on a hundred unit stake, so +150 means risk 100 to win 150. A minus number is what you must risk to win a hundred, so -200 means stake 200 to win 100. Anything at plus is an underdog, anything at minus is a favourite, and the switch happens at 2.00 decimal.
Divide 100 by a decimal price and you get the chance the bookmaker is pricing in. That single number is the most useful thing on this page, because it turns an abstract price into something you can argue with.
| Decimal | Fractional | American | Implied probability |
|---|---|---|---|
| 1.25 | 1/4 | -400 | 80.00% |
| 1.50 | 1/2 | -200 | 66.67% |
| 1.91 | 10/11 | -110 | 52.36% |
| 2.00 | 1/1 | +100 | 50.00% |
| 2.50 | 3/2 | +150 | 40.00% |
| 4.00 | 3/1 | +300 | 25.00% |
| 11.00 | 10/1 | +1000 | 9.09% |
Take a football match priced 2.10 home, 3.40 draw, 3.60 away. The implied probabilities are 47.6, 29.4 and 27.8, which comes to 104.8 percent. That extra 4.8 is the margin, the bookmaker edge baked into every price in the market. Nothing is wrong with the maths, the book is simply built to add up to more than certainty.
On a big football match you will see 3 to 5 percent. On a smaller league it drifts to 6 or 8. On novelty and in play markets it can reach double figures, and on an outright golf market it sits somewhere between 25 and 40 percent across the whole field. Lower is always better for you, and the difference compounds over a season far faster than any single winning bet.
Two euros of difference on a 2.10 against a 2.05 does not look like much. Over a hundred bets of fifty euros it is the difference between a small profit and a small loss. Holding accounts at three or four licensed books and taking the best price on the market you want is the one habit that improves results without needing you to be right more often.
A value bet is not a bet you think will win. It is a bet where your estimate of the chance is higher than the price implies. Those are different things, and the difference is the whole game.
If a price of 2.50 implies 40 percent and you think the real chance is 45, you have five points of edge. On a ten euro stake the expected value is one euro twenty five. You will still lose that bet more often than you win it, which is exactly why people give up on the idea long before it pays.
The calculator cannot tell you if your 45 percent is any good. Most people overrate the team they watch and underrate the one they have never seen. A useful discipline is to write your number down before you look at the price, because once you have seen 2.50 it is very hard to think 38 percent.
The Kelly criterion tells you the stake that maximises long run growth given your edge. Five points of edge at 2.50 works out at just over eight percent of your bankroll, which is an enormous bet. Because your probability estimate is itself uncertain, full Kelly overbets badly whenever you are slightly wrong. Quarter Kelly is the common compromise, and flat staking is perfectly respectable.
Nothing. That is the answer. A negative number means the price is worse than your own read, and the correct response is to shop for a better price or leave the market alone. No amount of confidence turns a bad price into a good one.
Accumulators are fun, they pay for the acca insurance offers that live on every sportsbook homepage, and they are the most expensive bet on the card. Both things are true at once.
Every leg carries the bookmaker margin, and combining legs multiplies them together rather than adding them. Four legs at 5 percent each does not cost you 5 percent, it costs roughly 19. That is why a four fold looks so generous and pays so rarely.
Four legs at 1.80, 2.10, 1.65 and 3.00 combine to 18.71. Ten euros returns 187 euros and change, which feels like a lot until you notice the implied probability is 5.3 percent. Roughly one in nineteen. The same forty euros spread across the four as singles returns about 74 euros if they all land, and still pays something when three of them do.
Small stakes for entertainment, or when a bookmaker is offering a genuine acca boost or insurance that hands back the margin they just took. Treat the boost as the product and the bet as the price of entry, not the other way around.
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Subtract one from the decimal price and turn what is left into a fraction. A price of 2.50 becomes 1.50, which is 3/2. The converter above does it for you and snaps the result to the fractions bookmakers actually use, so 1.91 comes out as 10/11 rather than 91/100.
It is the chance a price is pricing in, found by dividing 100 by the decimal odds. A price of 4.00 implies 25 percent. Add up the implied probabilities for every outcome in a market and you get more than 100 percent, and the surplus is the bookmaker margin.
A bet where your own estimate of the chance is higher than the price implies. It has nothing to do with how likely the bet is to win. A 20 percent shot priced at 6.00 is value, a 90 percent shot priced at 1.05 is not.
Full Kelly is mathematically optimal only if your probability estimate is exactly right, which it never is. Most people who use it bet a quarter of the recommended stake or less. Flat staking is a perfectly sound alternative and far easier to stick to.
Because the bookmaker margin on each leg multiplies rather than adds. Four legs at 5 percent margin each leaves roughly 19 percent with the bookmaker. The payout looks generous because the probability is tiny, not because the price is good.
Yes. They run entirely in your browser, nothing is sent anywhere and nothing is stored. All amounts are shown in euros.
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