Football betting odds do two jobs at once. They tell you how much a winning bet returns, and they express the bookmaker's view of how likely an outcome is. Once you can read both sides of a price, comparing markets becomes much easier. This guide explains the three common odds formats, how to convert between them, how to turn odds into an implied probability and why the probabilities in a market add up to more than 100%. The examples use round numbers so that the arithmetic is easy to follow.
The three common odds formats
Fractional odds are traditional in the UK and Ireland. A price of 5/2 means that a £2 stake wins £5 in profit, and the stake is returned on top. A price of 1/2 means the opposite: you need to stake £2 to win £1 in profit. When the first number is larger than the second, the outcome is considered less likely than not.
Decimal odds are standard across most of Europe and on many betting exchanges. They include the stake in the figure, so a price of 3.50 returns £3.50 for every £1 staked, which is £2.50 profit plus the original £1. Decimal odds are the easiest format for quick comparisons because a higher number always means a larger return.
American odds, also called moneyline odds, use a plus or minus sign. A positive price such as +250 shows the profit on a £100 stake. A negative price such as -200 shows how much you need to stake to win £100 in profit. The sign tells you at a glance whether an outcome is priced as the underdog or the favourite.
Converting between formats
All three formats describe the same price, so any one can be converted into the others. To turn fractional odds into decimal odds, divide the first number by the second and add one: 5/2 becomes 2.5 + 1 = 3.50. To turn decimal odds above 2.00 into American odds, subtract one and multiply by 100: 3.50 becomes +250. For decimal odds below 2.00, divide -100 by the decimal odds minus one: 1.50 becomes -100 / 0.5 = -200.
| Fractional | Decimal | American | Implied probability |
|---|---|---|---|
| 1/2 | 1.50 | -200 | 66.7% |
| 4/5 | 1.80 | -125 | 55.6% |
| Evens (1/1) | 2.00 | +100 | 50.0% |
| 6/4 | 2.50 | +150 | 40.0% |
| 5/2 | 3.50 | +250 | 28.6% |
| 4/1 | 5.00 | +400 | 20.0% |
| 9/1 | 10.00 | +900 | 10.0% |
From odds to implied probability
Implied probability is the chance of an outcome that a price suggests. With decimal odds the calculation is a single division: divide one by the odds and multiply by 100. Decimal odds of 2.50 give 1 / 2.50 = 0.40, or a 40% implied probability. With fractional odds, divide the second number by the sum of both numbers: 6/4 gives 4 / (6 + 4) = 0.40, the same 40%.
Implied probability is useful because it lets you ask a practical question. If you believe an outcome is more likely than the price suggests, the price looks generous to you; if you believe it is less likely, the price looks short. The odds do not tell you what will happen. They tell you what the price assumes.
Why a market adds up to more than 100%
Take a match with three outcomes priced at 2.10 for the home win, 3.40 for the draw and 3.60 for the away win. The implied probabilities are 47.6%, 29.4% and 27.8%, which add up to 104.8%. The extra 4.8% is the bookmaker's margin, often called the overround. It is built into every price in the market and is how a bookmaker covers its costs over many events.
A smaller overround means prices closer to the bookmaker's own estimate of the true chances. Comparing the total implied probability of the same market at different bookmakers is a quick way to see which prices carry the smallest margin.
Reading a match market
The main football market is the match result, sometimes shown as 1X2: 1 for the home win, X for the draw and 2 for the away win. Other common markets include both teams to score, the total number of goals over or under a line such as 2.5, and the correct score. Each market has its own set of prices, and each set carries its own margin. Markets with many possible outcomes, such as correct score, usually carry a larger overround than a two-way market such as over or under 2.5 goals.
Prices also move before kick-off. Team news, weather and the amount of money placed on each side can all shift the odds. A price you see in the morning may be different an hour before the match.
Keeping betting in proportion
Understanding odds helps you see what a bet costs and what it can return, but it does not change the outcome of a match. Decide on a budget before you bet, treat it as the cost of entertainment and use the deposit limits and time-outs that betting accounts provide. If betting stops being enjoyable, take a break and speak to an independent support service.
