How do decimal betting odds work?
Decimal odds show your total return for each 1 unit you stake, including the stake itself. At odds of 2.50, a £10 bet returns £25 if it wins: £15 profit plus your £10 back. To find the implied probability, divide 1 by the odds: 1 / 2.50 = 0.40, or 40%.
How do you calculate winnings from decimal odds?
Decimal odds are the standard format across Europe and on most betting apps, and they are the easiest to work with. There are two simple formulas:
- Total return = stake × odds
- Profit = stake × (odds − 1)
So a £20 bet at 1.75 returns £35 (£20 × 1.75), which is £15 profit plus your £20 stake. The same works in dollars or any other currency.
The lowest possible decimal odds are just above 1.00. Odds of 1.00 would mean you only get your stake back, so there would be no point in the bet.
What do decimal odds say about probability?
Every price hides a probability. The formula is: implied probability = 1 / decimal odds. Lower odds mean the bookmaker thinks the outcome is more likely.
| Decimal odds | Implied probability | Return on a £10 stake | Profit |
|---|---|---|---|
| 1.25 | 80.0% | £12.50 | £2.50 |
| 1.50 | 66.7% | £15.00 | £5.00 |
| 2.00 | 50.0% | £20.00 | £10.00 |
| 2.50 | 40.0% | £25.00 | £15.00 |
| 3.00 | 33.3% | £30.00 | £20.00 |
| 4.00 | 25.0% | £40.00 | £30.00 |
| 5.00 | 20.0% | £50.00 | £40.00 |
| 10.00 | 10.0% | £100.00 | £90.00 |
Odds of 2.00 are “evens”: you double your money if you win, and the implied chance is 50%.
Why do the probabilities add up to more than 100%?
Add up the implied probabilities of every outcome in a market and you will usually get more than 100%. The difference is the bookmaker’s margin, sometimes called the overround or “vig”.
Take a two-way market, such as Over/Under 2.5 goals, with both sides priced at 1.90:
- Over 2.5 at 1.90: 1 / 1.90 = 52.6%
- Under 2.5 at 1.90: 1 / 1.90 = 52.6%
- Total: 105.3%
If the bookmaker took no margin, a true 50/50 market would be priced at 2.00 on each side. Pricing both at 1.90 means every winning bet pays a little less than the fair rate. This is how bookmakers build a margin into odds, and it is why no format of odds is “free money”.
How do decimal odds compare with fractional and American odds?
UK bookmakers often show fractional odds, and US sportsbooks use American (moneyline) odds. They all describe the same price:
| Decimal | Fractional (UK) | American (US) | Implied probability |
|---|---|---|---|
| 1.25 | 1/4 | −400 | 80.0% |
| 1.50 | 1/2 | −200 | 66.7% |
| 2.00 | 1/1 (evens) | +100 | 50.0% |
| 2.50 | 3/2 | +150 | 40.0% |
| 3.00 | 2/1 | +200 | 33.3% |
| 5.00 | 4/1 | +400 | 20.0% |
To convert:
- Decimal to fractional: subtract 1 and write it as a fraction. 2.50 − 1 = 1.50, which is 3/2.
- Decimal to American (odds of 2.00 or more): (decimal − 1) × 100. For 3.00: 2 × 100 = +200.
- Decimal to American (odds below 2.00): −100 / (decimal − 1). For 1.50: −100 / 0.50 = −200.
How do you use decimal odds to judge value?
A bet has “value” when your honest estimate of the chance is higher than the implied probability. For example, odds of 2.50 imply 40%. If careful research suggests the real chance is closer to 45%, the price looks generous. If you think it is 35%, the price looks poor, even if the team is likely to play well.
Two cautions. First, your estimate can be wrong, and a value bet still loses often: at 45%, it loses more than half the time. Second, value only shows up over many bets, so stakes should stay small and steady.
Where BetGPT fits
BetGPT shows the odds for the main markets on each match screen, next to the recommended pick and a confidence level. You can ask the suggested follow-up “Is the price worth it?” to compare the odds with what the stats suggest. It helps you read a price more clearly, but it cannot remove the uncertainty that every price contains.
18+. Betting involves risk; no prediction is guaranteed. If gambling stops being fun, visit BeGambleAware or call 1-800-GAMBLER in the US.