Odds

Odds are compiled by bookmakers and represent the likelihood of a particular outcome occurring and how much a bettor stands to win should their selection prove successful.

Odds are at the heart of betting, and the ability to read and interpret them is a key tool in any bettor's armoury.

Odds can be used to determine favourites and underdogs, calculate payout, returns, implied probability and betting margins and determine value.

There are three different types of odds - fractional odds, decimal odds and American odds - and the type of odds displayed by a bookmaker depend on whereabouts you are in the world.

Fractional odds

Fractional odds are traditionally favoured by British and Irish bookmakers. They are written in fraction form with a slash (/) or hyphen (-), and show the ratio of returns to stake.

Fractional odds consist of a numerator - the first number - and a denominator - the second number.

Fractional odds present the profit the bettor makes per stake placed. The numerator demonstrates the returns and the denominator shows the stake.

For example, odds of 5/2 would see returns of £5 for every £2 stake placed.

Fractional odds of 1/1 are also referred to as evens. Outcomes with fractional odds of over 1/1 - where the first number is bigger than the second - are considered underdogs, while outcomes with fractional odds under 1/1 - where the first number is smaller than the second- are considered favourites.

Decimal odds

Decimal odds are the odds favoured by bookmakers in continental Europe, Canada, Australia and New Zealand. They provide odds in decimal form.

Decimal odds represent the total payout for every £1 placed on the bet, meaning your initial stake is also included.

For example, if odds of 1.97 were quoted, a £1 bet would see a total payout of £1.97.

Favourites have decimal odds under 2.00 and underdogs have decimal odds of over 2.00. Odds of exactly 2.00 are evens.

American odds

American odds are the odds favoured by American bookmakers. The odds are quoted as either positive or negative and are accompanied with a plus or minus symbol to show the favourite and underdog.

Positive odds represent the underdog in a bet, meaning this outcome is considered less likely to happen than not. The positive odds indicate how much money would be won from a $100 bet.

For example, if odds of +300 were quoted, then a $100 bet would see returns of $300 and a total payout of $400.

Negative odds represent the favourite in a bet, meaning this outcome is considered more likely to happen than not. The negative odds represent how much money must be bet to see returns of $100.

For example, if odds of -300 were quoted, then a $300 bet would see returns of $100 and a total payout of $400.

Odds of +100 are commonly referred to as evens.

Using odds to calculate probability

Implied probability is the conversion of betting odds into a percentage to show the expected probability of an outcome. It is used by bettors to determine whether the odds offered by bookmakers are good value or not.

Calculating implied probability is really simple but is slightly different depending on your preferred odds format.

Converting decimal odds to implied probability

In order to calculate implied probability using decimal odds, simply divide 1 by the decimal odds and multiple it by 100.

(1 / decimal odds) * 100 = implied probability

For example, if the odds for Manchester United to beat Chelsea at home were 1.50, the implied probability of the home win would be 66.7%.

(1 / 1.5) * 100 = 66.66%

Converting fractional odds to implied probability

To calculate implied probability using fractional odds, divide the denominator by the sum of the denominator + numerator, and then multiply by 100.

denominator / (denominator + numerator) * 100 = implied probability

For example, if the odds for Manchester United to beat Chelsea at home were 1/2, the implied probability of the home win would be 66.7%.

(1 / (1+2)) * 100 = 66.66%

Converting American odds to implied probability

If you use American odds then you will need to calculate negative and positive odds using slightly different formulas.

Negative odds

To calculate implied probability for negative American odds, divide the odds by the sum of the odds + 100 and then multiple by 100.

Negative American odds / (Negative American odds + 100) * 100 = implied probability

For example, if the odds for Manchester United to beat Chelsea at home were -200, the implied probability of the home win would be 66.7%.

200 / (200 + 100) * 100 = 66.66%

Positive odds

To calculate implied probability for positive American odds, divide 100 by the sum of the odds + 100 and multiply by 100.

100 / (positive American odds + 100) * 100 = implied probability

For example, if the odds for Chelsea to beat Manchester United away from home were 200, the implied probability of the away win would be 33.3%.

100 / (200 + 100) * 100 = 33.33%

Using odds to calculate returns

Odds can also be used to calculate returns - the profit made from a successful bet. Again, the means by which this is calculated differs according to your odds format preference.

Calculating returns with decimal odds

To calculate returns using decimal odds, the following formula is used.

(Stake * decimal odds) - stake

For example

  • Barcelona vs Real Madrid - Barcelona to win at odds of 1.85 with a £20 stake

20 * 1.85 = 37

37 - 20 = 17

Returns = £17

Calculating returns with fractional odds

To calculate returns using fractional odds, the following formula is used:

Stake * (numerator / denominator)

For example

5 * (3 / 1) = 15

Returns = £15

Calculating returns with American odds

To calculate returns on a positive odds bet, the following formula is used:

Stake * (odds / 100)

For example

  • Arsenal vs Chelsea - Arsenal to win odds of +250 with a $10 bet stake

10 * (250 / 100) = 25

Therefore returns would be $25.

To calculate returns on a negative odds bet, the following formula is used:

Stake * ((100 / (odds * - 1))

For example

  • Liverpool vs Everton - Liverpool to win at odds of -400 with a $10 stake

10* ((100 / (-400 * -1)) = 2.5

Therefore returns would be $2.50.

Converting odds

Should you wish to convert odds from the version provided by the bookmaker to your odds format preference, this can be achieved with a little bit of maths on your behalf.

Converting decimal odds into fractional odds

There is no formula to convert decimal odds into fractional odds, just a little bit of maths to do instead.

Step 1) Convert decimal odds into fractional form by subtracting 1 from the decimal

Step 2) This number becomes the numerator (the first number), and use the number 1 as the denominator (the second number)

Step 3) Convert the fraction into its simplest form by finding the nearest whole number that the numerator divides into.

Step 4) The number by which you times the numerator by to make it into a whole number becomes the denominator.

For example

  • Atalanta vs Roma - over 2.5 goals at odds of 3.40

Step 1) 3.40 - 1 = 2.40

Step 2) 2.4/1

Step 3) 2.4 * 5 = 12

Step 4) 5/12

Converting fractional odds into decimal odds

To convert fractional odds into decimal odds, the following formula is used:

(numerator / denominator) + 1

For example

  • Atletico Madrid vs Real Madrid - both teams to score at odds of 5/6

(5 / 6) + 1 = 1.83

Converting American odds into decimal odds

In order to convert American odds into decimal odds, the following formulas are used.

For positive odds, the formula for converting American odds into decimal odds is as follows:

Odds / 100 + 1

For example

  • Atalanta vs Roma - over 2.5 goals at odds of +150

150 / 100 + 1 = 2.50

For negative odds, the formula for converting American odds into decimal odds is as follows:

100 / Odds + 1

For example

  • Inter Milan vs AC Milan - Inter to win at odds of -250

100 / 250 + 1 = 1.40

Converting decimal odds into American odds

To convert decimal odds of over 2.00 into American odds, the following formula is used:

(Decimal - 1) * 100

For example

  • Juventus vs Turin - both teams to score at odds of 3.35

(3.35 - 1) * 100 = +235

To convert decimal odds of under 2.00 into American odds, the following formula is used:

-100 / (decimal - 1)

For example

  • Roma vs Atalanta - Roma to win at odds of 1.65

-100 / (1.65 - 1) = -154

Converting American odds into fractional odds

In order to convert American odds into fractional odds, the odds are arranged in a certain way and then reduced to their simplest form.

For positive odds, to convert American odds into fractional odds, the odds are arranged as follows:

Odds/100

And then reduced into simplest form.

For example

  • Barcelona vs Real Madrid - Real Madrid to win at odds of +300

300/100 reduces down into 3/1

For negative odds, to convert American odds into fractional odds, the odds are arranged as follows:

100/odds

And then reduced into simplest form.

For example

  • Atletico Madrid vs Valencia - Atletico Madrid to win at odds of -250

100/250 reduces down to 2/5

Converting fractional odds into American odds

Fractional odds above 1/1 will provide positive American odds. To convert fractional odds of above 1/1 into American odds, the following formula is used:

(numerator / denominator) *100

For example

  • Barcelona vs Valencia - over 2.5 goals at odds of 7/4

(7 / 4) * 100 = +175

Fractional odds of under 1/1 will provide negative American odds. To convert fractional odds under 1/1 into American odds, the following formula is used:

-100 / (numerator / denominator)

For example

  • Juventus vs Roma - Juventus to win at odds of 1/4

-100 / (1 / 4) = -400

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