Devigging

Devigging is the process of stripping the bookmaker's margin (the vig, or vigorish) out of a betting market to estimate the true, fair probability of each outcome. Because posted odds always bake in a built-in profit margin, the implied probabilities across a market sum to more than 100%. Devigging removes that surplus so the numbers reflect what the bookmaker actually thinks will happen, rather than what it needs to charge to guarantee a hold. The most common method is the multiplicative approach: convert every price to its implied probability, add them up to find the overround, then divide each probability by that total so they sum back to 100%. The result is a set of "no-vig" or "fair" odds you can compare against other books or against your own model. Worked example: a two-way market is priced at 1.91 for each side. Each implies 1 / 1.91 = 52.36%, so the two sum to 104.72% — a 4.72% overround. Divide each by 1.0472 and both fair probabilities become 50.0%, giving true odds of 2.00. If a sharper book instead offers one side at 2.05 (48.8% fair after devigging), you have identified a potential value bet worth roughly 2.4% of edge. For affiliates and sharp bettors, devigging a market-leading book's closing line is a standard way to gauge whether an operator's price is genuinely competitive or merely disguised by heavier margin. Compare with vig, vigorish, overround, implied probability and no-vig odds.