**What is probability ?**

Probability is a quantitative measure of the likelihood of a given event. If we are certain that an event will occur it is assigned a probability of 100%. If we are certain that an event will not happen it is assigned a probability of 0%. Other events which are neither certain to occur nor certain not to occur are assigned probabilities between 0% and 100%. If an event has a probability of 50% then it is as likely to happen as not to happen. An event with a probability of 10% is not likely to happen while an event with a probability of 90% is likely to happen.

**Example 1** Suppose you take a coin from your pocket and toss it in the air. Assuming that it is a fair coin, there are two possible outcomes, heads or tails, and each outcome is equally possible. Therefore, the probability of it being heads is 50% and the probability of it being tales is also 50%.

**Example 2** Using a full deck of cards and drawing one card at random the probability of the card being a spade is 1 in 4, there are four suits in a deck of which one is spades. To express this as a percentage you divide the required outcome by the number of possible outcomes and multiply by 100%. So the probability of a spade being drawn at random is (1 / 4) X 100% = 25%

**How do odds relate to probability ?**

First of all let me explain that there are two ways of expressing odds, fractional odds and decimal (sometimes known as digital) odds.

Fractional odds look like this, 2/1 4/1 11/2

Decimal odds look like this, 3 5 6.5

Odds are simply a way of converting the probability of an event happening into the amount of money you will receive back if you bet on it.

Using the card example above, there is a 25% chance that a spade will be picked at random.

In fractional odds, there are 3 chances you will choose wrongly and 1 chance you will choose correctly, therefore the odds are 3/1. If you put £10 on at 3/1 and are correct you will win 3 X £10 so you will now have £40 as your original £10 is returned for winning bets. To convert a %age to fractional odds divide 100% by the probability %age and subtract 1. In this example,

100% / 25% = 4

4 - 1 = 3

The odds are 3/1

In decimal odds things are much simpler to work out. The odds are simply 100% divided by the probability %age. Using the same card example,

100% / 25% = 4

The odds are 4

Therefore, if you put £10 on at odds of 4 you will now have 4 X £10 = £40.

Below is a table of odds and percentages.

%age |
Fractional Odds |
Decimal Odds |
%age |
Fractional Odds |
Decimal Odds |
---|---|---|---|---|---|

99.01 |
1/100 |
1.01 |
50 |
1/1 |
2 |

98.04 |
1/50 |
1.02 |
47.62 |
11/10 |
2.1 |

97.06 |
1/33 |
1.03 |
44.44 |
5/4 |
2.25 |

96.15 |
1/25 |
1.04 |
42.11 |
11/8 |
2.38 |

95.24 |
1/20 |
1.05 |
40 |
6/4 |
2.5 |

94.12 |
1/16 |
1.06 |
38.10 |
13/8 |
2.63 |

92.31 |
1/12 |
1.08 |
36.36 |
7/4 |
2.75 |

90.91 |
1/10 |
1.1 |
34.78 |
15/8 |
2.88 |

89.89 |
1/8 |
1.12 |
33.33 |
2/1 |
3 |

87.50 |
1/7 |
1.14 |
30.77 |
9/4 |
3.25 |

85.71 |
1/6 |
1.16 |
28.67 |
5/2 |
3.5 |

84.61 |
2/11 |
1.18 |
26.67 |
11/4 |
3.75 |

83.33 |
1/5 |
1.2 |
25 |
3/1 |
4 |

81.82 |
2/9 |
1.22 |
23.08 |
10/3 |
4.33 |

80 |
1/4 |
1.25 |
22.22 |
7/2 |
4.5 |

77.78 |
2/7 |
1.29 |
20 |
4/1 |
5 |

76.92 |
3/10 |
1.3 |
18.18 |
9/2 |
5.5 |

75 |
1/3 |
1.33 |
16.67 |
5/1 |
6 |

73.33 |
4/11 |
1.36 |
15.39 |
11/2 |
6.5 |

71.43 |
2/5 |
1.4 |
14.29 |
6/1 |
7 |

69.23 |
4/9 |
1.44 |
12.5 |
7/1 |
8 |

66.67 |
1/2 |
1.5 |
11.11 |
8/1 |
9 |

65.22 |
8/15 |
1.53 |
9.09 |
10/1 |
11 |

63.64 |
4/7 |
1.57 |
7.69 |
12/1 |
13 |

61.90 |
8/13 |
1.62 |
5.88 |
16/1 |
17 |

60 |
4/6 |
1.67 |
4.76 |
20/1 |
21 |

57.89 |
8/11 |
1.73 |
3.85 |
25/1 |
26 |

55.56 |
4/5 |
1.8 |
2.94 |
33/1 |
34 |

52.38 |
10/11 |
1.91 |
1.96 |
50/1 |
51 |

50 |
1/1 |
2 |
0.99 |
100/1 |
101 |

Please note that for betting purposes there are no odds for 0% or 100%. This is because if an event has a probability of 100% nobody would take your bet because they are guaranteed to lose. Likewise, if an event has a probability of 0% then you are guaranteed to lose.

There is a quick and simple online tool for converting moneyline, fractional and decimal odds at OddsConverter.co.uk