Understanding Odds
How to read American, Decimal, and Fractional odds.
Odds are the language of sports betting. They tell you two things: how much you can win and the implied probability of that outcome. Master reading odds, and you'll instantly understand any betting line.
Three Odds Formats
The same probability can be expressed three ways:
Same Odds, Different Formats
| American | Decimal | Fractional | Meaning |
|---|---|---|---|
| +150 | 2.50 | 3/2 | Bet $100, win $150 |
| -150 | 1.67 | 2/3 | Bet $150, win $100 |
| +100 | 2.00 | 1/1 | Bet $100, win $100 |
American Odds (Moneyline)
Most common in the US. Based on $100 bets.
Positive Numbers (+)
Show profit on a $100 bet:
Underdog. You risk $100 to win $250.
Negative Numbers (-)
Show how much to bet to win $100:
Favorite. You risk $175 to win $100.
Decimal Odds
Common in Europe and Australia. Shows total return per $1 bet.
Multiply your stake by the decimal to get total return.
Strategy Insight
Fractional Odds
Traditional UK format, especially for horse racing. Shows profit relative to stake:
- 5/1 = Win $5 for every $1 bet
- 1/4 = Win $1 for every $4 bet
- 11/8 = Win $11 for every $8 bet
Converting Between Formats
Good to Know
- Positive: (American ÷ 100) + 1
- Negative: (100 ÷ |American|) + 1
Calculating Implied Probability
Odds imply how likely the sportsbook thinks an outcome is:
Odds and Implied Probability
| American | Implied Probability | True Meaning |
|---|---|---|
| -300 | 75% | Very likely to happen |
| -150 | 60% | More likely than not |
| +100 | 50% | Even odds |
| +200 | 33% | Underdog |
| +500 | 16.7% | Long shot |
The Vig Hidden in Odds
Sportsbooks don't offer fair odds. The implied probabilities on both sides add up to more than 100%:
The extra 4.8% is the sportsbook's built-in profit margin.
Strategy Insight
Worked Example: Comparing Three Books on the Same Game
Suppose the Lakers are playing the Celtics and you want to bet the Lakers moneyline. DraftKings posts Lakers at +145, FanDuel posts +150, and BetMGM posts +155. On a $100 bet, the difference between +145 and +155 is $10 of profit — an extra 6.9 percent on every winning ticket. Over 100 bets that is $1,000 left on the table for someone who does not line shop. The implied probabilities are 40.8 percent, 40.0 percent, and 39.2 percent respectively, meaning BetMGM is giving you the most generous price while DraftKings has baked in the most margin. Always place your bet at the best available number, not the first one you see.
Removing the Vig to Find a Fair Line
To estimate what a fair, no-vig line would be, add both sides' implied probabilities, then divide each by that sum. For a -110 versus -110 line (52.38% + 52.38% = 104.76%), the de-vigged probability for each side is 52.38 / 104.76 = 50.0 percent. That is mathematically equivalent to a pick-em game. Comparing the de-vigged line at a soft book against the posted line at a sharp book is a foundational method for identifying +EV spots, and it is why professional bettors spend so much time building consensus prices across multiple books.
Common Beginner Odds Mistakes
- Confusing +150 with 1.5x payout. +150 means $150 profit on $100 staked, for a total return of $250. Decimal 2.50 is the equivalent and makes this easier to see.
- Assuming a -200 favorite is safe. -200 implies a 66.7 percent win rate. One in three of those favorites will lose on average. Expect cold streaks.
- Stacking heavy favorites in a parlay. Four -300 favorites produce combined odds of roughly +97, which pays less than even money. The vig compounds and the house edge balloons.
Good to Know
Use our Universal Bet Calculator to instantly convert between American, Decimal, and Fractional odds and see exactly what you'll win.
Good to Know
Compare odds across sportsbooks to find the best price with BonusBell's Odds Comparison tool. See every book's line side by side and never overpay for a bet again.
Key Takeaways
- 1American odds: + shows profit on $100, - shows stake needed to win $100
- 2Decimal odds: multiply by stake for total return
- 3Fractional odds: numerator/denominator shows profit ratio
- 4Implied probability reveals how likely books think outcomes are
- 5Both sides' probabilities exceed 100%—the difference is vig
Sources & References
- American to Decimal: positive = (American ÷ 100) + 1; negative = (100 ÷ |American|) + 1. Decimal to Fractional: (Decimal − 1) as fraction. Standard mathematical conversions, independently verifiable.
- Implied probability from American odds: positive = 100 ÷ (Odds + 100); negative = |Odds| ÷ (|Odds| + 100). Independently verifiable derivation from the definition of odds.
- Vig (overround) calculation: sum of implied probabilities on all outcomes minus 100%. A standard −110/−110 line produces 104.8% total implied probability, yielding ~4.5% hold. Independently verifiable.
- American Gaming Association (AGA), State of the States annual report. Referenced for US legal sports betting market context and odds format prevalence.
Mathematical claims are independently verifiable. BonusBell platform analysis reflects data from 220+ tracked platforms as of March 2026.