How betting odds work
Updated · 2 min read
Odds do two jobs: they tell you how much a bet pays, and they hint at how likely the bookmaker thinks the outcome is. Once you can switch between formats and probabilities, every market becomes easier to read.
Decimal odds
Decimal odds show the total return for each unit staked, including your stake. A 10 bet at 2.50 returns 25 if it wins: 15 profit plus the 10 stake.
Return = stake × odds. Profit = stake × (odds − 1).
Fractional and American odds
Fractional odds (common in the UK) show profit relative to stake: 3/2 means 3 profit for every 2 staked, the same as decimal 2.50.
American odds use 100 as the reference. A plus number is the profit on a 100 stake (+150 is decimal 2.50). A minus number is how much you must stake to win 100 profit (−200 is decimal 1.50).
| Decimal | Fractional | American | Implied probability |
|---|---|---|---|
| 1.50 | 1/2 | −200 | 66.7% |
| 2.00 | 1/1 (evens) | +100 | 50.0% |
| 2.50 | 3/2 | +150 | 40.0% |
| 4.00 | 3/1 | +300 | 25.0% |
In CADNEX you can switch between decimal, fractional, American, Hong Kong, Indonesian and Malay odds in Settings.
From odds to probability
Implied probability = 1 ÷ decimal odds. At 2.50 the price implies a 40% chance. If you believe the real chance is higher than 40%, the bet has value; if lower, it doesn’t.
The bookmaker margin
Add up the implied probabilities of every outcome in a market and you’ll get more than 100%. The extra is the margin (also called the overround or vig). In a two-way market priced 1.91 and 1.91, each side implies 52.4%, a total of 104.7%: a margin of about 4.7%.
The margin is why, over many bets, a bettor who picks at random loses roughly that percentage of what they stake. Lower margins are better for you; parlays multiply the margin of every leg.
Why odds move
- New information: team news, injuries, weather.
- Money: heavy betting on one side moves prices at real bookmakers.
- The live game: in play, every goal, break of serve or run of points changes the probabilities. CADNEX reprices every few seconds and pauses betting briefly after big moments.
Common questions
What do odds of 2.00 mean?
Evens: a winning bet doubles your stake (10 returns 20). The implied probability is 50%.
Are higher odds better?
Higher odds pay more but are less likely to win. What matters is whether the odds are higher than the true chance justifies.
What is the vig or overround?
The bookmaker’s built-in margin: the amount by which the implied probabilities of all outcomes add up to more than 100%.