How we calculate fair odds for football markets

Every sportsbook adds a margin (vig, juice, overround) to their odds. To find +EV bets, we need to remove that margin and estimate the "fair" probability.

Four main devigging methods:

1. Multiplicative. Simplest. Divide each implied probability by the sum of all implied probabilities. Fast but biases favourites downward and longshots upward.

2. Additive. Subtract equal margin from each leg. Better for balanced markets like 1X2 but breaks at extreme prices.

3. Power. Adjust probabilities by raising to a power and rescaling. Handles favorite-longshot bias gracefully.

4. Shin. Models the proportion of "insider" bettors. Statistically the most accurate for high-margin markets like 1X2 and player props.

The strikey.io +EV scanner now picks the method automatically: Shin for 3-way markets (1X2) where favourite-longshot bias matters most, Power for 2-way markets (totals, BTTS, Draw No Bet), and Multiplicative only as a fallback for unusual shapes. Each row's "Fair %" tooltip shows which method produced it.