How to read betting odds
Decimal, fractional and American odds explained — what you get back, and the probability hidden in the price.
Betting odds tell you two things at once: how much a winning bet returns, and the implied probability the bookmaker has assigned to that outcome. The same price can be written three ways — decimal, fractional or American — and you can switch between them with our odds converter.
The three odds formats
| Format | Example | How to read it |
|---|---|---|
| Decimal | 2.50 | Total return per £1 staked, stake included. £10 → £25 back (£15 profit). |
| Fractional | 6/4 | Profit relative to stake. £4 staked wins £6 profit, plus your £4 back. |
| American | +150 | Profit on a 100 stake (underdog). −200 instead means stake 200 to win 100 (favourite). |
Those three examples are the same price: 2.50 = 6/4 = +150. Decimal is the standard on UK and European online bookmakers; fractional is the traditional UK format; American (moneyline) is used in the US. To convert fractional to decimal, divide and add 1: 6 ÷ 4 = 1.5, + 1 = 2.50.
The probability hidden in the odds
Every price implies a probability — the break-even chance the odds represent. From decimal odds it is simply 1 ÷ decimal, shown as a percentage:
2.00 → 50% · 2.50 → 40% · 4.00 → 25% · 1.50 → 66.7%
So odds of 2.50 imply the outcome has roughly a 40% chance. This is the single most useful thing to read from a price: shorter odds = higher implied chance and a smaller return; longer odds = lower implied chance and a bigger return.
Why the percentages add up to more than 100%
Add up the implied probabilities for every outcome in a market and you will get morethan 100%. That excess is the bookmaker’s margin (also called the overround or vig) — it is how they build in their edge.
Example: a two-way market priced 1.90 / 1.90 implies about 52.6% on each side — together 105.3%. That extra 5.3% is the margin. Because of it, the true chance of each outcome is a little lower than the implied figure, and the long-run return to a bettor is negative by roughly the margin. That is exactly why an independently-calculated probability is useful for understanding a price — not for beating the margin, which no method reliably does.
Favourites, underdogs and where a model fits
A “favourite” is just the outcome with the shortest odds (highest implied chance); an “underdog” has longer odds. Shorter odds are not inherently safer bets and longer odds are not inherently better — the return is scaled to the chance.
xgprophet’s model estimates each outcome’s probability directly from expected goals (xG) and recent form, using a Poisson model — and then expresses it as a fair price(1 ÷ probability, with no margin added). Comparing that fair probability with the probability implied by a bookmaker’s odds shows where the two disagree. That is useful context for understanding a match — it is not a betting recommendation, and every call we make is settled openly on our public accuracy record.
Frequently asked questions
- What is the difference between decimal and fractional odds?
- Decimal (2.50) is your total return per £1 including stake; fractional (6/4) is profit relative to stake. They are the same price — 6/4 = 2.50. Convert by dividing the fraction and adding 1.
- What do +150 and −200 mean in American odds?
- American odds against a 100 stake. +150 = win 150 profit from a 100 stake (underdog, decimal 2.50). −200 = stake 200 to win 100 profit (favourite, decimal 1.50). +100 is evens.
- Do shorter odds mean a better bet?
- No — they just mean a higher implied chance and a smaller return. Whether a price is good depends on whether the true chance beats the implied chance, which no one knows for sure. A model can estimate it, but it is not a guarantee. Information only, not betting advice.