Using the Odds Calculator
The odds calculator is an essential tool for bettors and statisticians alike, designed to instantly convert between the four most common formats of betting odds: American, Decimal, Fractional, and Implied Probability. By inputting just one known value, you can see how much a bet will pay out and understand the underlying mathematical probability of an event occurring.
This tool is particularly useful when comparing lines across different sportsbooks that may use different formats, or when you want to determine if a bet offers "value" based on your own predictions.
- American Odds
- Used primarily in the US. Positive numbers (+) indicate how much profit you make on a $100 bet. Negative numbers (-) indicate how much you must bet to make a $100 profit.
- Decimal Odds
- Common in Europe and Australia. This number represents the total payout (Stake + Profit) for every $1 wagered.
- Fractional Odds
- Traditional in the UK. The numerator (top) is the potential profit, while the denominator (bottom) is the amount you must stake.
- Implied Probability
- The percentage chance of the outcome occurring as suggested by the odds, excluding the "vig" or sportsbook margin.
How It Works: The Formulas
To convert between formats manually, the odds calculator uses specific algebraic formulas depending on the starting value. Decimal odds serve as the "bridge" for most conversions.
American to Decimal
If Positive: (Odds / 100) + 1 | If Negative: (100 / |Odds|) + 1
Decimal to Implied Probability
Probability = (1 / Decimal Odds) × 100
Calculation Example
Example: You see a team listed at +150 (American Odds) and you want to bet $50.
Step-by-step conversion:
- Decimal: (150 / 100) + 1 = 2.50
- Fractional: (2.50 – 1) = 1.5, which is 3/2
- Probability: (1 / 2.50) × 100 = 40%
- Profit: $50 × (2.50 – 1) = $75.00
- Total Payout: $50 + $75 = $125.00
Common Questions
What are "Even Money" odds?
Even money occurs when the potential profit equals your stake. In American odds, this is +100 or -100. In decimal, it is 2.00. In fractional, it is 1/1. The implied probability of even money is 50%.
Why doesn't the probability add up to 100%?
When using an odds calculator on sportsbook lines, you will notice the total probability of all outcomes (e.g., Win/Loss) exceeds 100%. This extra percentage is the "overround" or "vig," which is the fee the bookmaker charges for taking the bet.
Which format is best?
Decimal odds are often considered the most efficient for calculation because they automatically include the return of the stake. However, American odds are standard in the US for point spreads and money lines.