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Strip the sportsbook's vig out of any 2-way or 3-way market. Enter both sides' American odds; the calculator returns the fair (no-vig) probabilities. Use no-vig probability as the baseline for edge identification.
Paste both sides of a two-way market (or three sides of a three-way market). The calculator strips the sportsbook's vig and returns the no-vig (fair) probabilities the market thinks. No-vig probability is what you compare your model against to find edge.
Sportsbook prices include vig, the book's built-in commission. When you add both sides of a two-way market, the implied probabilities sum to MORE than 100% (typically 102-110%). The extra is the vig. To find the fair probability the market actually thinks, divide each side's implied probability by the total. That removes the vig.
Market: Yankees -150 vs Red Sox +130.
The market thinks the Yankees win 58.0% of the time, not 60.0%. The 2 percentage points were vig.
Your bet has edge when your win probability estimate exceeds the no-vig market probability by 3+ percentage points. Example: your model says Yankees 62%; no-vig market says 58%; your edge is 4 points. The bet is +EV at -150. Size with the Kelly calculator.
Lower vig means better prices for you. Line-shopping across 3+ books captures small no-vig probability advantages on every pick.
Some markets (soccer, hockey 3-way) have three outcomes: home win, draw, away win. The calculator handles 3-way: enter all three sides' American odds and the math divides each by the total to give no-vig probabilities for all three.
A devig calculator removes the sportsbook's vig (commission) from both sides of a market to compute the fair no-vig probability each side wins. It's the baseline for edge identification: your model's probability vs the no-vig market probability.
Compute implied probability for each side from American odds. Add them up (they'll sum to over 100% because of vig). Divide each side's implied probability by the total. The result is the no-vig probability for each side. Example: -150/+130 sums to 103.48%; 60.00/103.48 = 57.98% no-vig favorite.
Vig (vigorish or juice) is the sportsbook's commission baked into the odds. At a -110/-110 market, both sides imply 52.4% probability, summing to 104.8%. The 4.8% excess is the overround. The book's built-in margin works out to about 4.5% of each bet (1 - 1/1.0476). It gives the book a built-in margin, so with balanced action on both sides the book profits whichever side wins.
Standard US sportsbooks (DraftKings, FanDuel, BetMGM) carry 4-6% vig on MLB moneylines. Sharp books (Pinnacle, Circa) run 2-3%. Soft markets (props, novelties) can run 7-12% vig. Lower vig = better prices for the bettor.
Compare your model's win probability to the no-vig probability from the calculator. If your model says 62% and no-vig says 58%, you have 4 points of edge. Size the bet with the Kelly calculator. Anything below 2-3 points of edge isn't worth betting due to estimation noise.