Proofset AcademyModule 2 · Sports bettingLesson 2.3Free · 25 min

Reading odds

Odds are not just a number next to a name. They are a disguised probability: behind 1,80 lies an estimate of the player's chance. Learning to read them means moving from the bookmaker's language to the language of probability.

Part 1

Decimal odds

Across most of Europe and on Proofset, odds are written in decimal format: 1,80, 2,00, 3,50. Decimal odds tell you by how much the stake is multiplied if the bet wins, stake included. The lower the odds, the more likely the outcome is considered.

Low odds: 1,10 to 1,60

The outcome is considered very likely. These are usually the odds of a clear favourite.

Around 2,00

The outcome is considered about as likely as its opposite: an evenly balanced match.

High odds: 3,00 and above

The outcome is considered unlikely. These are the odds of an underdog.

Never below 1,00

Odds of 1,00 would mean a certain outcome. There is no such thing: in tennis, even a very strong favourite can lose.

Part 2 · Your turn

One set of odds, three formats

In the United Kingdom, odds are read as fractions; in the United States, as numbers with a + or − sign. These are three ways of writing the same thing. Drag the decimal odds slider.

1,80
Decimal1,80
Fractional4/5
American−125
FormatHow to read itConvert to decimal
DecimalThe stake is multiplied by the odds, stake included.—
FractionalWhat the stake returns on top of itself: 4/5 means 4 for every 5 staked.4/5 → 4 ÷ 5 + 1 = 1,80
American +For an underdog: what 100 staked returns, on top of the stake.+150 → 150 ÷ 100 + 1 = 2,50
American −For a favourite: what you must stake to win 100 on top.−125 → 100 ÷ 125 + 1 = 1,80
Part 3

Implied probability

All odds hide a probability, called the implied probability. You get it by dividing 1 by the odds:

implied probability = 1 ÷ odds

Odds 1,25

1 ÷ 1,25 = 80 %. The odds assume this player wins 4 matches out of 5.

Odds 1,80

1 ÷ 1,80 = 55,6 %. A little more than one match in two.

Odds 4,00

1 ÷ 4,00 = 25 %. One match in four.

Note: this probability still contains the bookmaker's margin. If you add up the implied probabilities of the two players in a match, you always exceed 100 %. Lesson 2.4 shows how to remove this margin. The calculator in Proofset's Tools tab does these calculations automatically.

Part 4 · Animation

The odds scale

Odds are not read like a distance. Between 1,10 and 1,50, the implied probability drops by more than 24 points. Between 5,00 and 10,00, it drops by only 10. Small odds change the chance a lot; large odds change it very little.

Part 5 · Your turn

Reading an odds screen

Here is a fictitious odds screen, like those on a licensed site. Click on one of the odds to translate it into a probability and find out who the favourite is.

Click on one of the odds.

Why it matters for a bet

  • Always read odds as a probability. “1,80” tells you nothing; “55,6 %” tells you what the odds assume.
  • Low odds are not a guarantee. Odds of 1,25 still assume one defeat in five, margin included.
  • Implied probability is not the true probability. It contains the margin (lesson 2.4), and it can be wrong (lesson 2.5).
Part 6

Test yourself

7 questions. You need 6 correct answers to pass the lesson.

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