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Odds Calculator: One Price in Three Formats, and What It Really Means
Type a price in decimal, fractional or American odds and the odds calculator shows it in the other two formats and as an implied probability. Add every outcome of a market to see the bookmaker's margin and the fair odds without it.
Written by: Owen Treadgold·Checked by: Maren Holt·Updated:
Odds are written three ways around the world, and each way hides the same two numbers: what you win for your stake, and how likely the bookmaker thinks the outcome is. The odds calculator turns any price into all three formats and into a probability, and it measures the margin that every sportsbook builds into a market.
Odds calculator
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Three ways to write the same price
| Decimal | Fractional | American | Implied probability |
|---|---|---|---|
| 1.50 | 1/2 | -200 | 66.7% |
| 1.91 | 10/11 | -110 | 52.4% |
| 2.00 | Evens | +100 | 50.0% |
| 2.50 | 6/4 | +150 | 40.0% |
| 3.00 | 2/1 | +200 | 33.3% |
| 5.00 | 4/1 | +400 | 20.0% |
| 11.00 | 10/1 | +1000 | 9.1% |
Decimal odds include the stake: 2.50 returns 2.50 for every 1 staked. They are the standard in Europe, Australia and most of the world, and the easiest for arithmetic.
Fractional odds show the profit against the stake: 6/4 wins 6 for every 4 staked. They are traditional in Britain and Ireland, above all in horse racing.
American odds use 100 as the base. A positive number shows the profit on a stake of 100; a negative number shows the stake needed to win 100. They are standard in the United States and Canada.
How to use the odds calculator
- Choose the format you will type in. Switching it converts the prices already entered.
- Type the price in Price to convert to see it in decimal, fractional and American odds and as an implied probability.
- To measure a market, set the number of outcomes and type the price of each one: three for a football match, two for a tennis match.
The results show the market's margin, and the table shows each outcome's implied probability, its fair probability after the margin is removed, and its fair odds.
Implied probability
Implied probability is one divided by the decimal odds. It is the chance a price suggests, with the bookmaker's margin still inside it. It is the most useful number in betting, because it lets you compare a price with your own view: if you think a team wins half the time and the odds imply 40%, the price is generous by your estimate; if they imply 60%, it is not.
The bookmaker margin
Add up the implied probabilities of every outcome in a market and the total is always above 100%. The excess is the margin, sometimes called the overround or vig, and it is how a sportsbook earns money whichever outcome wins.
- A Premier League match result priced 2.30, 3.40 and 3.20 implies 43.5%, 29.4% and 31.3%, a total of 104.1% and a margin of about 4.1%.
- An NBA spread at -110 on both sides implies 52.4% twice, 104.8% in total, a margin of about 4.8%.
- A golf outright with a hundred and fifty runners often adds up to well over 120%.
Lower is better for the bettor. The margin is thinnest where the most money is bet and widest in props, small leagues and long-range outrights, which is the pattern described on the best odds betting sites page.
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Fair odds
Fair odds take the margin out. The odds calculator divides each implied probability by the market total, so a 104% market is scaled back to 100%, and turns the result back into odds. It is the standard quick method, and it is an estimate: in practice bookmakers often load more margin onto long shots than onto favourites, which is known as the favourite-longshot bias. On a heavy favourite the fair price may be a little shorter than the calculator shows, and on an outsider a little longer.
SportsbookSportsbook and casino in one accountOpen sportsbook18+ · read the terms before your first depositWhen the numbers are useful
Comparing sites. The same match at two sportsbooks, measured with the odds calculator, shows which one takes less margin.
Checking your own view. Turn your estimate into odds and compare it with the price on offer.
Reading unfamiliar formats. A tip in American odds, a racecard in fractions, a bet slip in decimals: one tool for all three.
Spotting a price that moved. Odds that drift from 2.00 to 2.20 look like a small change. In probability terms the market has gone from 50% to about 45%, which is a real shift in opinion, usually caused by team news or money. Turning prices into percentages makes such moves easier to read than the odds alone.
Odds formats by sport and region
Most sportsbooks let you switch the format in the account settings, and the choice changes nothing about the bet itself. Still, each sport has its habits. Racing in Britain and Ireland is quoted in fractions, from 11/10 to 100/1. North American sports, from the NFL to the NHL, are quoted in American odds, with the -110 line as the everyday price on spreads and totals. Football, tennis and esports are quoted in decimals almost everywhere else. If you follow tipsters from different countries, the odds calculator saves you converting in your head.
The calculator for full bet slips, from doubles to a Lucky 15 and each way, is the bet calculator. How each sport sets its prices is on the sports betting hub.
For the operators themselves, read our comparison of betting sites without verification: verification triggers, withdrawal caps and deadlines.
More in the same section: Arbitrage calculator, Dutching calculator and all betting calculators.
How do I convert fractional odds to decimal?
Divide the first number by the second and add one. 5/2 is 2.5 plus 1, which is 3.50. Evens, 1/1, is 2.00.
How do I convert American odds to decimal?
For positive odds, divide by 100 and add one: +150 is 2.50. For negative odds, divide 100 by the number without its minus sign and add one: -200 is 1.50.
What is implied probability?
The chance a price suggests, before the margin is taken out: one divided by the decimal odds. Odds of 2.50 imply 40%.
What is the bookmaker margin?
The amount by which the implied probabilities of all outcomes in a market add up to more than 100%. A football match priced 2.30, 3.40 and 3.20 adds up to about 104.1%, a margin of about 4.1%.
What are fair odds?
The odds with the margin removed. The odds calculator spreads the margin in proportion to each price, which is a common estimate; bookmakers do not always load it evenly.