Sports Betting Odds Calculator
Convert American, decimal, or fractional odds into implied probability or potential payout. Use it before placing a bet to compare lines across sportsbooks or spot value in the market.
About this calculator
All odds formats express the same underlying probability but in different notations. American odds above zero (e.g. +150) show profit on a $100 stake; negative odds (e.g. -110) show what you must risk to win $100. Both convert to decimal odds via: decimal = (odds / 100) + 1 for positives, or (100 / |odds|) + 1 for negatives. Fractional odds (e.g. 3/2) become decimal by dividing numerator by denominator and adding 1. Implied probability is then: P = 1 / decimal_odds × 100. Potential payout equals bet_amount × decimal_odds, which includes your original stake returned.
How to use
Suppose you see American odds of +150 on a team and want to know the implied probability and payout on a $50 bet. Step 1 — Convert to decimal: (150 / 100) + 1 = 2.50. Step 2 — Implied probability: 1 / 2.50 × 100 = 40.00%. Step 3 — Potential payout: $50 × 2.50 = $125.00 (includes your $50 stake, so profit is $75). Enter 150 as the odds value, select American format, enter 50 as the bet amount, and choose your desired output.
Frequently asked questions
How do I convert American odds to implied probability?
American odds reflect how much you win relative to a fixed stake. For positive American odds, divide 100 by (odds + 100) to get implied probability — e.g. +200 gives 100/300 ≈ 33.3%. For negative odds, divide the absolute value by (|odds| + 100) — e.g. -150 gives 150/250 = 60%. This probability tells you how often the bookmaker expects the outcome to occur, though it is inflated by the vig (bookmaker margin).
What is the difference between decimal odds and fractional odds?
Decimal odds represent your total return per unit staked, including the stake itself — odds of 2.50 mean you get back $2.50 for every $1 wagered. Fractional odds (common in UK horse racing) show only the profit relative to stake — 3/2 means $3 profit for every $2 staked, equivalent to decimal 2.50. Decimal odds are generally easier to compare and are standard on most international exchanges like Betfair.
Why does the implied probability from bookmaker odds add up to more than 100%?
When you sum the implied probabilities across all outcomes in a market, the total typically exceeds 100% — this excess is called the overround or vig. It represents the bookmaker's built-in margin, ensuring profitability regardless of the outcome. A typical sports market runs at 105–110%, meaning bettors collectively receive less than fair value. Comparing implied probability against your own estimated probability helps identify bets where you hold an edge over the house.