Odds do two jobs at once: they tell you the payout, and they encode how likely the book thinks an outcome is. Learn to read both and every line becomes far more legible. There are three common formats, and they all describe the same thing.
The three formats
American (+/−)
The default in the US. A minus number (−150) is the favorite — it’s how much you must stake to win $100. A plus number (+150) is the underdog — it’s how much you win on a $100 stake.
Decimal
Common in Europe and on exchanges. The number is your total return per $1 staked, stake included. Decimal 2.50 means a winning $10 bet returns $25 ($15 profit).
Fractional
Traditional in the UK. 3/2 means you win $3 for every $2 staked. The left number is profit, the right is your stake.
Turning odds into a probability
Every price implies a win percentage. For a negative American line, divide the odds by the odds plus 100; for a positive line, divide 100 by the odds plus 100. So −150 implies 150 ÷ 250 = 60%, and +150 implies 100 ÷ 250 = 40%. Decimal is even simpler: implied probability is 1 divided by the decimal odds.
One bet, three ways
- American
- −150
- Decimal
- 1.67
- Fractional
- 4/6
- Implied probability
- ≈ 60%
Notice the implied probabilities across a full market add up to more than 100% — that gap is the vig. Strip it out to see the fair price.
Why the probability matters more than the payout
Once you can read the implied probability, you can compare it to your own estimate of the outcome. When your number is higher than the price implies, the bet may carry positive expected value. That comparison — your read versus the market’s read — is the whole game, and it’s exactly what Statly’s Edge Score is built to surface.