Odds Explained
What are odds?
Odds represent the likelihood of an outcome as estimated by a sportsbook. They also determine how much you win if your bet is correct. There are three common formats: decimal, American, and fractional.
Understanding odds is the foundation of making informed betting decisions. Without knowing how to read odds, you can't calculate your potential returns, compare value across bookmakers, or determine whether a bet offers positive expected value.
Decimal odds
Decimal odds are the most straightforward format, commonly used in Canada, Europe, and Australia. They represent the total return per $1 wagered, including your stake.
Example: A $10 bet at odds of 2.50 returns $25 total ($15 profit + $10 stake).
The higher the decimal number, the less likely the sportsbook thinks the outcome is, and the more you stand to win. Decimal odds of 1.50 imply roughly a 67% chance, while odds of 4.00 imply about a 25% chance.
Decimal odds are especially popular in the analytics community because they make math simple: multiply stake by odds to get total payout. No need to handle positive and negative cases like American odds.
American odds
American odds use a plus (+) or minus (-) sign. They're the standard format in the United States.
- Negative (-) odds show how much you need to bet to win $100. Example: -150 means bet $150 to win $100 profit.
- Positive (+) odds show how much you win on a $100 bet. Example: +200 means a $100 bet wins $200 profit.
The key threshold is -100 / +100 (even money). Anything with a negative sign is favored to happen; anything positive is considered an underdog.
Decimal to American: If decimal ≥ 2.00, American = (decimal - 1) × 100. If decimal < 2.00, American = -100 / (decimal - 1).
Example: Decimal 2.50 = +150. Decimal 1.50 = -200.
Fractional odds
Fractional odds are traditional in the UK and Ireland. They show profit relative to stake. For example, 5/2 means you win $5 for every $2 staked (plus your stake back).
While less common in North America, you may encounter them on some international sportsbooks or in horse racing. The equivalent decimal odds for 5/2 would be 3.50 (5 ÷ 2 + 1).
To convert fractional to decimal: divide the numerator by the denominator and add 1. To convert decimal to fractional: subtract 1 and express as a fraction (e.g., 2.50 becomes 1.50 = 3/2).
Quick reference table
1.50 decimal = -200 American = 1/2 fractional (67% implied)
2.00 decimal = +100 American = 1/1 fractional (50% implied)
2.50 decimal = +150 American = 3/2 fractional (40% implied)
3.00 decimal = +200 American = 2/1 fractional (33% implied)
4.00 decimal = +300 American = 3/1 fractional (25% implied)
Try it yourself
Use the calculator below to convert between odds formats and see implied probability, payout, and profit for any stake.
Odds Calculator
Implied probability
Implied probability converts odds into a percentage that represents the sportsbook's estimate of the outcome happening.
Example: Odds of 2.00 = 50% implied probability. Odds of 4.00 = 25%. Odds of 1.50 = 66.7%.
If you add up the implied probabilities of all outcomes in a market, the total will exceed 100%. The excess is the sportsbook's margin (vig). For example, if a two-outcome market shows implied probabilities of 55% and 50%, the total is 105% — the 5% is the sportsbook's edge.
The vig explained
The vig (vigorish, or juice) is how sportsbooks make money. Instead of offering true odds, they shade the line slightly in their favor. Understanding vig is critical because it means you need to do better than break-even to profit.
A market with a 5% vig means the sportsbook keeps roughly 5 cents on every dollar wagered over time. Lower-vig markets (found on betting exchanges or sharp books) are better for bettors because your break-even point is lower.
Comparing odds across bookmakers
Different sportsbooks offer different odds on the same event. Shopping for the best line can significantly impact your returns over time. Even a small improvement in odds compounds across many bets.
This is exactly what OddsLab does — it compares odds across 15+ regional bookmakers and highlights the best available price for each pick.
Why line shopping matters more than you think
Research shows that consistently getting the best available odds can be worth 1–3% in additional ROI over the course of a season. For someone placing hundreds of bets, that can mean the difference between being profitable and breaking even.
The closing line (the last odds available before an event starts) is widely considered the most accurate price. If you consistently get better odds than the closing line (positive CLV), it suggests your timing and selection process are strong.