Convert any odds format
Type a number in any of the four boxes. The other three update live, and the payout table at the bottom tracks your stake.
Common bookmaker lines at a glance
These six prices cover almost every market you will see, from heavy favourites down to clear underdogs. The last column shows the full return on a 10 unit stake.
| Decimal | Fractional | American | Implied % | Return on 10 |
|---|---|---|---|---|
| 1.50 | 1/2 | -200 | 66.67% | 15.00 |
| 1.91 | 10/11 | -110 | 52.36% | 19.10 |
| 2.00 | 1/1 (Evens) | +100 | 50.00% | 20.00 |
| 2.50 | 3/2 | +150 | 40.00% | 25.00 |
| 3.50 | 5/2 | +250 | 28.57% | 35.00 |
| 5.00 | 4/1 | +400 | 20.00% | 50.00 |
How the conversion maths works
Decimal is the simplest format and sits at the centre of every calculation. The decimal price tells you how many units come back for every one unit staked, winnings and stake included. Implied probability is the direct inverse of decimal, so a 2.00 line implies 50 percent, a 1.50 line implies about 66.67 percent, and a 5.00 line implies 20 percent. The formula is implied = 1 divided by decimal.
Fractional odds, the traditional British format, split the profit from the stake. A line of 3/2 means a 2 unit stake pays 3 units of profit on top. To turn A/B into decimal, divide A by B and add 1. So 3/2 becomes 1.5 plus 1 which equals 2.50. 10/11 becomes 0.909 plus 1 which equals about 1.91, the shop price for a close two-way market.
American odds work in two directions around the Evens line. A positive American number such as +150 shows the profit on a 100 unit stake, so the decimal is 150 divided by 100 plus 1, giving 2.50. A negative American number such as -200 shows how much you must stake to win 100 units, so the decimal is 100 divided by 200 plus 1, giving 1.50. The sign flips exactly at 2.00 decimal, which is +100 or -100 depending on the house convention.
The Evens boundary is where American books change signs because the maths runs out of a clean 100 unit base. Below 2.00 the favourite side needs a bigger stake to win 100, so the minus sign appears. Above 2.00 the underdog side wins more than 100 off a 100 stake, so the plus sign appears. Decimal and fractional have no such flip because they always speak in multiples of the stake.
Implied probability is also how you spot the book's margin, often called the overround or vig. Add the implied probabilities on both sides of a two-way market. A fair market totals 100 percent. Most books price a two-way to around 104 to 108 percent, and that extra 4 to 8 percent is the house edge. The lower the overround, the better the price for the punter, and this is where comparing books before you bet pays off.
Worked example
Scenario. You spot a 2.20 decimal price on a tennis favourite and you want to see what that looks like in every format before you commit a 10 unit stake.
Decimal to fractional. 2.20 minus 1 equals 1.20. Written as a simple ratio that is 6/5, which most UK shops will round to 6/5 or display as 1.20 on an exchange.
Decimal to American. Because 2.20 sits above 2.00, we use the plus formula. (2.20 minus 1) times 100 equals 120, so the American line is +120.
Decimal to implied probability. 1 divided by 2.20 equals 0.4545, so the implied probability is 45.45 percent. The market is telling you this outcome needs to land roughly 45 times in every 100 identical fixtures to be a fair price.
Payout. A 10 EUR stake at 2.20 returns 22 EUR total, which is 10 EUR of your own stake back plus 12 EUR of net profit. Hit this exact scenario above 45.45 percent of the time and you are long-run profitable at that price.
Frequently asked questions
Why do American books use plus and minus signs?
American sportsbooks grew out of a base-100 unit system. Plus odds show the profit you make on a 100 unit stake, while minus odds show how much you must risk to win 100 units. It is a shorthand that fits US sports culture, but the maths underneath is identical to decimal. Our converter does the sign flip for you at the 2.00 Evens line.
What is a decent decimal line and what is a terrible one?
There is no fixed answer because odds reflect probability, not value. A 1.20 line on an obvious favourite can be excellent if the real chance is 90 percent, and a 5.00 shot can be awful if the real chance is only 10 percent. What matters is the gap between the implied probability and your own honest estimate of how often the outcome lands. Our implied column is there so you can make that call quickly.
What is overround and how do I spot it?
Overround is the book's built-in margin. In a two-way market, add the implied probability of both sides. If the total is 104 percent, the book has a 4 percent edge. The lower the overround, the better the price you get. Exchanges often run at 101 to 102 percent, soft books at 104 to 106 percent, and some local shops at 108 percent or higher. A quick overround check across books is the fastest way to find the strongest line on any fixture.
Can I combine odds for a parlay or accumulator?
Yes, and the formula is simpler than it looks. Multiply the decimal odds of every leg to get the parlay decimal. A 2.00 leg combined with a 1.50 leg gives 2.00 times 1.50 which equals 3.00. Our calculator handles single prices, but you can convert each leg to decimal here and multiply them in your head or in a spreadsheet. The implied probability also multiplies, which is why big parlays carry a huge house edge even when every leg looks fair.
Why is implied probability important for finding value?
Implied probability turns odds into a yes-or-no question you can answer with your own research. If a book implies 40 percent and you believe the real chance is 50 percent, the bet has positive expected value. If the book implies 55 percent and you believe the real chance is 40 percent, it does not matter how big the payout looks, it is a losing bet in the long run. The converter is a sanity check before you click confirm.
Can I use this converter for casino side-bets?
Yes, provided the side-bet pays out in standard odds. Blackjack side-bets, roulette straight-up numbers and keno picks all have a quoted payout that maps cleanly to decimal. House odds are usually tilted against you, so expect implied probabilities that are much lower than the real mathematical chance. The gap is the house edge, and this tool makes it visible in seconds.
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