Definition
No-vig odds (fair odds) remove the book's margin to reveal true implied probabilities. Convert each side from American to implied probability, sum them, then divide each by the sum to normalize to 100%. The result is what each side "truly" costs without the tax. No-vig lines are critical for identifying which side of a market has value and for calculating closing-line value. Books that post no-vig markets (Pinnacle, some exchanges) are the gold standard for fair pricing.
Worked Example
Market: Team A −130, Team B +110. Implied probabilities: A = 130 ÷ 230 = 56.52%; B = 100 ÷ 210 = 47.62%. Sum = 104.14% (4.14% vig). No-vig: A = 56.52 ÷ 104.14 = 54.28%; B = 47.62 ÷ 104.14 = 45.73%. No-vig odds: A = −118.6, B = +118.6. True price has 9.4 cents less juice than posted.
Why It Matters
Comparing your bet price to no-vig closes tells you whether you got value. Beating the no-vig close consistently is the clearest signal of a winning process.