The central idea
No-vig odds estimate prices after removing the displayed margin. Proportional normalisation rescales every implied probability so the adjusted market totals 100%.
Fair probabilityᵢ = implied probabilityᵢ ÷ total implied probability
Worked example
Two prices of 1.91 imply 52.36% each. Dividing each figure by the 104.71% market total gives 50%. The proportional no-vig price for each side is therefore 2.00.
Limits of the calculation
Proportional normalisation is one removal method. It assumes the displayed margin is distributed proportionally and does not prove that the adjusted probabilities are true.