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Free calculator
Calculate the overround across a set of odds.
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Market odds
Enter decimal odds for every outcome in the market.
Enter the odds for every outcome in a market, including draws or additional options. The calculator sums the implied probabilities and reports the overround percentage, plus each outcome's margin-adjusted fair price.
The amount by which implied probabilities across all outcomes exceed 100%. A book with 105% total implied probability charges a 5 percent margin.
Price the same market at each book and run both through the calculator. The lower overround wins. Margins vary by league and market, not just by book.
Fair probability estimates start from margin-free odds. Knowing each book's margin tells you how far its prices sit from fair and where value can appear.