How to read betting odds
Three formats say the same thing in different words. Convert any of them to an implied probability in one step, see how much of that probability is bookmaker margin, and read the number that actually decides whether a bet is worth making.
Decimal odds of 2.50 mean a winning £1 stake returns £2.50 in total — your stake plus £1.50 profit. The implied probability is 1 ÷ 2.50 = 40%. Fractional odds of 3/2 and American odds of +150 describe exactly the same price. Once you can convert to implied probability, all three formats become one number you can compare against your own estimate.
The three formats, side by side
Every format encodes the same price. Which one you see depends on where you are: decimal in Europe and Australia, fractional in the UK and Ireland, American in North America.
| Decimal | Fractional | American | Implied probability | Return on £10 |
|---|---|---|---|---|
| 1.20 | 1/5 | −500 | 83.3% | £12.00 |
| 1.50 | 1/2 | −200 | 66.7% | £15.00 |
| 2.00 | 1/1 (evens) | +100 | 50.0% | £20.00 |
| 2.50 | 3/2 | +150 | 40.0% | £25.00 |
| 4.00 | 3/1 | +300 | 25.0% | £40.00 |
| 9.00 | 8/1 | +800 | 11.1% | £90.00 |
Converting in one step
Decimal is the format worth thinking in, because the conversion to probability is a single division:
implied probability = 1 / decimal odds1 / 2.50 = 0.40, i.e. 40%.To go the other way — from your own probability estimate to the price you would need:
fair decimal odds = 1 / your probabilityIf you think an outcome is 45% likely, the fair price is 1 / 0.45 = 2.22.Fractional odds are profit relative to stake, so 3/2 means three units of profit for every two staked. Add the stake back to get decimal: 3/2 → (3÷2) + 1 = 2.50. American odds above +100 are the profit on a 100 stake; below −100 they are the stake needed to win 100.
| From | To decimal |
|---|---|
| Fractional a/b | (a ÷ b) + 1 |
| American positive (+X) | (X ÷ 100) + 1 |
| American negative (−X) | (100 ÷ X) + 1 |
The part of the price that is not probability
Add up the implied probabilities of every outcome in a market and you will get more than 100%. That is not an error. The excess is the bookmaker's margin — the reason the business exists.
A typical three-way football market:
| Outcome | Decimal odds | Implied probability |
|---|---|---|
| Home win | 2.10 | 47.6% |
| Draw | 3.40 | 29.4% |
| Away win | 3.80 | 26.3% |
| Total | 103.3% |
The 3.3 percentage points above 100 are the margin. Removing it to recover what the market actually believes is called de-vigging, and doing it wrong is the most common error in amateur analysis — see de-vigging methods for how it is done and where it goes astray.
Margin is charged on every bet you make, winning or losing. At 3.3% across a three-way market, a bettor with no edge at all loses roughly that share of turnover over time. It is the single largest fixed cost in betting, and the only one you can reduce by shopping around — see line shopping.
What do the odds not tell you?
A price is the market's opinion, weighted by money. It is a good opinion — bookmaker closing lines are among the most accurate publicly available forecasts of sporting outcomes. But knowing the price tells you nothing about whether to take it.
A bet is worth making only when your own probability estimate is higher than the de-vigged market probability, by enough to cover the margin and the uncertainty in your estimate. That comparison — not the size of the odds — is the whole job. Long odds are not "value" and short odds are not "safe"; both are just prices.
Check any of this against our record
Every signal CONSENSUS publishes carries the bookmaker odds fixed before the event starts and the settled result afterwards — including the drawdowns and the losing runs. The running total is on the front page and every entry is in the log.