About the Odds Converter
Betting sites show the same odds in different ways, and it is easy to misread them when you switch between a UK, US or European site. Type odds in any of the three formats, decimal like 3.50, fractional like 5/2 or American like +250, and this converter shows all three together with the implied probability. Add your stake to see the profit and total return if the bet wins. If you also paste the odds for every outcome in a market, it works out the bookmaker's margin and the fair chances once that margin is removed. It is a converter only and does not give betting advice.
Updated October 2026
How to use the Odds Converter
- 1Choose the format of the odds you have.
- 2Type the odds, for example 5/2, +250 or 3.50.
- 3Optionally enter a stake to see the profit and return.
- 4Optionally paste the decimal odds of every outcome in the market.
- 5Read the three formats, the implied probability and the margin.
The three formats
Decimal odds show the total you get back for each 1 staked, including the stake, so 3.50 returns 3.50 for 1. Fractional odds show the profit compared with the stake, so 5/2 means 5 profit for every 2 staked. American odds show the profit on a 100 stake for underdogs and the stake needed to win 100 for favourites.
All three describe the same price. Converting is useful when you compare bookmakers or read an article from another country, and the implied probability gives a common scale.
Reading the margin
- Add the implied probabilities of every outcome in a market.
- A fair two-way market adds to exactly 100 percent.
- A total of 105 percent means a 5 percent margin.
- Dividing each probability by the total gives the fair chances.
- Lower margins mean better value for the bettor on average.
Related tools
The Probability Calculator and the Expected Value Calculator show how to judge whether a price is fair, while the Kelly Criterion Calculator explains stake sizing when you believe you have an edge. For card and dice questions, the Dice Probability Calculator covers outcomes you can count. Betting involves risk, and this page makes no promise of profit.
Features
- Decimal, fractional and American in one place
- Implied probability
- Profit and total return for your stake
- Bookmaker margin (overround) from a full market
- Fair chances with the margin removed
- Clear messages for odds typed wrongly
- Free and private
Frequently asked questions
How do I convert fractional to decimal odds?
Divide the top number by the bottom and add 1. Odds of 5/2 are 5 divided by 2, which is 2.5, plus 1, giving 3.50.
What do American odds mean?
A plus number such as +250 is the profit on a 100 stake. A minus number such as -200 is the stake needed to win 100.
What is implied probability?
It is 1 divided by the decimal odds. Decimal odds of 4.00 imply a 25 percent chance, before any bookmaker margin.
What is the bookmaker margin?
The sum of the implied probabilities for all outcomes is above 100 percent. The excess is the margin, also called the overround, which is how the bookmaker builds in profit.
Why are my American odds rejected?
They must start with plus or minus and be at least 100 in size. Odds between -100 and +100 do not exist in that format.
Are the converted odds exact?
Decimal and American values are exact. Fractional odds are shown as the simplest fraction within a denominator of 100, which can be an approximation for some decimals.
Is this betting advice?
No. It only converts numbers. Gambling carries a risk of loss and you should only stake money you can afford to lose.