Football Betting Odds Explained: Decimal, Fractional and American
Odds are the price of a bet. They tell you how much you collect if you win, and, read the other way round, how likely the bookmaker thinks the outcome is. Every value bet starts with reading that price correctly, and the same price can be written in three different formats depending on the country.
1. Decimal Odds
The format used across continental Europe, Australia and on every exchange. The number is your total return per unit staked, stake included. At 2.50, a 10 stake returns 25: 15 of profit plus your 10 back. The implied probability is simply 1 divided by the odds, so 2.50 means 1 / 2.50 = 40%. Because the maths is this direct, decimal is the format used throughout this site.
2. Fractional Odds
The traditional UK and Ireland format, written as 3/2 and read as three to two. The fraction is your profit relative to the stake, so a 10 stake at 3/2 wins 15 of profit and returns 25 in total. To get decimal odds, divide the fraction and add 1: 3 / 2 + 1 = 2.50. Evens is 1/1, odds-on prices such as 1/2 are below 2.00 in decimal, and odds-against prices such as 4/1 are above it.
3. American (Moneyline) Odds
Used in the United States, it is always quoted around a 100 unit stake. A positive number is the profit on a 100 stake: +150 wins 150, which is 2.50 in decimal (1 + 150 / 100). A negative number is the stake needed to win 100: -200 means staking 200 to win 100, which is 1.50 in decimal (1 + 100 / 200). +100 and -100 are both the same even-money price, 2.00.
4. Converting Between Formats
Whatever the format, it is the same price, and decimal is the common denominator. Convert to decimal first and the implied probability follows in one step. The table shows the same prices in all three formats, with the probability they imply.
Equivalent odds in the three formats and the probability they imply
Decimal
Fractional
American
Implied probability
1.50
1/2
−200
66.7%
2.00
1/1
+100
50.0%
2.50
3/2
+150
40.0%
3.00
2/1
+200
33.3%
5.00
4/1
+400
20.0%
5. Implied Probability and the Bookmaker Margin
Add up the implied probabilities of every outcome in a market and a fair price would give exactly 100%. Bookmakers price the total above 100%, and the excess is their margin, also called the overround. In the example below the three 1X2 outcomes add up to 104.8%, a margin of 4.8%. Dividing each implied probability by the total strips the margin out and gives the fair probability: the home win drops from 47.6% to 45.4%, which is fair odds of 2.20 instead of the 2.10 on offer. That gap is what you must beat before a bet has any value.
1X2 market: implied probability and fair probability once the margin is removed
Outcome
Odds
Implied probability
Fair probability
Home win
2.10
47.6%
45.4%
Draw
3.40
29.4%
28.1%
Away win
3.60
27.8%
26.5%
Total
–
104.8%
100.0%
6. Convert and Compare with the Calculator
Doing these conversions by hand is slow and easy to get wrong. The odds converter at https://www.StatsForBetting.com turns any price into its implied probability, and the statistics tool shows the historical probability for the same market. Compare the two: if the historical rate is clearly above the probability the odds imply, you have a candidate value bet.
