How to Convert Betting Odds — Complete Guide
Betting odds come in several different formats depending on where you are in the world and which platform you use. European sportsbooks typically display decimal odds, American books use moneyline format, and UK bookmakers prefer fractional odds. Prediction markets like Polymarket and Kalshi express outcomes as prices between $0 and $1. Understanding how to convert between these formats is essential for any bettor who wants to compare value across platforms.
Decimal Odds (European)
Decimal odds are the simplest format to understand. They represent the total payout per dollar wagered, including your original stake. For example, decimal odds of 2.50 mean that a $1 bet returns $2.50 total ($1.50 profit plus your $1 stake). To find the implied probability from decimal odds, divide 1 by the decimal odds: 1 / 2.50 = 0.40, or 40%. Decimal odds are always greater than or equal to 1.00, where 1.00 represents a 100% probability event.
American Odds (Moneyline)
American odds use a baseline of $100. Positive odds (like +150) tell you how much profit you make on a $100 bet, so +150 means $150 profit. Negative odds (like -200) tell you how much you need to bet to win $100, so -200 means you need to wager $200 to profit $100. To convert from American to decimal: for positive odds, divide by 100 and add 1 (e.g., +150 becomes 2.50). For negative odds, divide 100 by the absolute value and add 1 (e.g., -200 becomes 1.50).
Fractional Odds (UK)
Fractional odds express your profit relative to your stake. Odds of 3/2 (read as "three to two") mean you profit $3 for every $2 wagered. To convert to decimal, divide the numerator by the denominator and add 1: 3/2 + 1 = 2.50. Common fractional odds include "evens" (1/1), "odds-on" (anything less than 1/1 like 1/2), and "odds-against" (anything greater than 1/1 like 5/1).
Implied Probability
Every set of odds implies a probability that the event will occur. This is called the implied probability. Converting odds to implied probability allows you to compare the sportsbook's estimate with your own assessment. If you believe the true probability is higher than what the odds imply, you have found a value bet. The formula is straightforward: implied probability = 1 / decimal odds. For a market with a 2% vig, the sum of implied probabilities across all outcomes would be 102% rather than exactly 100%.
Prediction Market Prices
Prediction markets like Polymarket, Kalshi, and PredictIt price outcomes as contracts that pay out $1 if the event occurs and $0 if it does not. A contract priced at $0.40 implies a 40% probability. This format is equivalent to the implied probability expressed as a decimal between 0 and 1. The beauty of prediction market prices is their simplicity: the price IS the probability. This makes cross-platform comparison with sportsbook odds especially useful for finding pricing discrepancies.
Why Convert Between Odds Formats?
The primary reason to convert odds is to compare prices across different platforms. A soccer match might be listed at 2.10 on a European sportsbook, +110 on an American book, and priced at $0.48 on Polymarket. Converting everything to implied probability (47.6%, 47.6%, and 48.0%) reveals that Polymarket is pricing this outcome slightly higher. Tools like the OddsBridge odds converter make this comparison instant, saving you time and helping you find the best value for every bet.
Common Odds Conversions
Some conversions come up so often that experienced bettors memorize them. Even money is 2.00 decimal, +100 American, 1/1 fractional, and 50% probability. A strong favorite at -300 American is 1.33 decimal, 1/3 fractional, and 75% probability. A longshot at +500 is 6.00 decimal, 5/1 fractional, and 16.67% probability. Knowing these benchmarks helps you quickly assess whether odds represent value without needing a calculator every time.
Tips for Using This Tool
Our odds converter auto-detects the format you enter. Type "2.50" for decimal, "+150" or "-200" for American, "3/2" for fractional, or "40%" for probability. Results update instantly as you type, so you can quickly iterate through different odds. Use the preset buttons for common benchmarks. Bookmark this page for quick access during live betting sessions when speed matters.