Odds education
How Odds Are Calculated
Understand how betting odds are calculated, including implied probability, bookmaker margin and decimal, fractional and American formats.
Market focus
Odds → %
Guide type
Education
Keywords
4 terms
Betting checklist
Read the market, compare the price, size the stake, then track the result.
1
Odds are probability with margin
Bookmakers price outcomes from estimated probability, then add margin. Decimal odds of 2.00 imply 50%, while 1.50 implies about 66.7%.
2
Formats explained
Decimal odds show total return per unit. Fractional odds show profit relative to stake. American odds show how much you win on + odds or need to stake on - odds.
- Decimal 2.50 returns 2.50 for every 1 staked.
- Fractional 3/2 means 1.5 profit per 1 staked.
- American +150 equals decimal 2.50.
3
Why margin matters
If all implied probabilities in a market add up to more than 100%, the extra percentage is bookmaker margin. Lower-margin markets generally give bettors better value.