Odds Format Conversion Formulas
American to Decimal
If American ≥ 0: Decimal = (American / 100) + 1
If American < 0: Decimal = (100 / |American|) + 1
Examples:
+150 → 2.50 | -110 → 1.909 | -200 → 1.50 | +300 → 4.00
Decimal to American
If Decimal ≥ 2.0: American = (Decimal − 1) × 100
If Decimal < 2.0: American = −100 / (Decimal − 1)
Examples:
2.50 → +150 | 1.909 → −110 | 1.50 → −200 | 4.00 → +300
Fractional to Decimal
Decimal = (Numerator / Denominator) + 1
Examples:
3/2 → 2.50 | 10/11 → 1.909 | 1/2 → 1.50 | 3/1 → 4.00
Implied Probability
Implied % = (1 / Decimal) × 100
Decimal = 100 / Implied %
Note: Sportsbook implied probs sum to >100% due to juice (overround).
Which Format Should You Use?
American odds are standard at US sportsbooks. Positive numbers show profit on $100 wagered; negative numbers show how much you must wager to win $100.
Decimal odds represent the total return per unit staked (including your stake). Multiply decimal odds by your stake to get total payout. Popular in Europe and Australia.
Fractional odds show net profit relative to stake. 3/1 means you profit $3 for every $1 staked. Common in UK horse racing markets.
Implied probability translates odds directly into a win percentage — the most intuitive format for comparing your model's estimates to the market price.
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