Implied probability: how to turn betting odds into a percentage

Every price can be turned into a percentage. With decimal odds:

Implied probability = 1 ÷ decimal odds

Multiply by 100 to read it as a percentage. If your odds are in another format, convert them to decimal first (see how betting odds work).

Implied probability also tells you your break-even rate. If you keep betting at 2.50, you need to win more than 40% of those bets just to not lose money. At 1.60 you need more than 62.5%. That's a useful reality check on short prices.

To go the other way, from a probability to the fair price, use 1 ÷ probability. A 25% chance has a fair price of 1 ÷ 0.25 = 4.00.

In a fair market, the chances of all outcomes would add up to exactly 100%. A bookmaker's prices always add up to more. The surplus is called the margin, overround or vig, and it's how the bookmaker makes money whatever the result.

You'll also see the margin expressed as a payout percentage, which is 1 ÷ the total. Here that's 1 ÷ 1.048 = 95.4%: on average, the market pays back about £95.40 for every £100 staked across all outcomes.

Two-way markets work the same way. A common price on both sides of an over/under line is 1.91 / 1.91. Each side implies 52.4%, and the total is 104.7%, a margin of about 4.7%. Without the margin, both sides would be priced at 2.00.

Here is the same calculation on a real match from today's schedule:

Raw implied probabilities overstate every outcome a little. To estimate what the bookmaker really thinks, you normalise them: divide each one by the total so they add up to 100%. This is the simplest method (proportional), and it's good enough for most football markets.

A short cut for fair odds: fair odds = bookmaker odds × total. For the home side, 2.10 × 1.0481 = 2.20.

Proportional normalising spreads the margin evenly. In reality bookmakers often load a bit more margin onto long shots (the favourite-longshot bias), so the fair chance of a big outsider is usually slightly lower than this method suggests. For beginners and for most match markets, the simple method is fine.

It's natural to read 2.00 as "a coin flip". But it's only 50% in a market with no margin. Take a two-way market priced 2.00 / 1.80:

So the bookmaker actually rates side A at about 47%, not 50%. The 2.00 price is the fair price (about 2.11) trimmed to include the margin. The same logic applies to every price you see: the raw implied chance is always a little too high.

Implied probability is the bridge between a price and your own judgement.

• Compare with your own estimate. If you think a team wins 50% of the time and the price is 2.30 (43.5%), the price is bigger than it "should" be. That gap is what value betting is built on.
• Compare bookmakers. Add up the implied chances of a market at different bookmakers. The lower the total, the smaller the margin and the better the deal for you. Our bookmakers page is a good starting point.
• Sanity-check short prices. A 1.20 shot implies 83.3%. Ask yourself honestly whether the team really wins five matches in every six like this one.
• Read the market's view. Fair probabilities give you a neutral starting point before you look at form, injuries and the numbers on our stats pages or today's predictions.

• Treating implied probability as the "true" chance. It's the bookmaker's estimate plus margin, not a fact. Bookmakers are good, but not perfect.
• Forgetting to remove the margin when reading the market. In the example above, the raw 47.6% overstates how likely the bookmaker thinks a home win is; the fair figure is 45.4%. To make a profit, though, you still have to beat the raw 47.6%, because that's the price you're paid at.
• Adding probabilities from different bookmakers. A margin is calculated within one bookmaker's market. Mixing the best price from several bookmakers is a different exercise (see sure bets).
• Ignoring the break-even rate. Backing lots of 1.50 favourites feels safe, but you need to win two out of three just to break even.
• Rounding too early. Keep three or four decimals while you calculate; round only the final answer.

Now that you can turn odds into percentages, see how they work in the most popular football market in 1X2 betting, or learn how fair prices are combined in double chance.