Two sides, more than 100%
−110 / −110 implied each = 110 / 210 = 52.38% sum = 104.76% overround = 4.76% // the excess over 100% hold = 1 − 1/sum = 4.55% // book margin on balanced action
The overround is how far the probabilities overshoot 100%. The hold is the share of total money the book keeps if action is perfectly balanced. Both describe the same margin from different angles.
Removing the vig
The simplest method — proportional normalisation — divides each side's implied probability by the total:
fair A = implied A / (implied A + implied B)
- Prices: −150 / +130.
- Implied: 60.0% and 43.5%. Sum 103.5%.
- Fair: 58.0% / 42.0% → fair prices -138 / +138.
Proportional normalisation assumes the margin is spread evenly. In practice books often load more margin on long shots (the favourite–longshot bias), so other methods (power, Shin) can give slightly different fair numbers. Treat no-vig figures as estimates, especially on one-sided or thin prop markets.
Why it matters for props
Player prop markets often carry more margin than main-line markets, and many are offered one-sided (only the over, or only "yes"). When the other side is not shown you cannot compute the vig directly — which makes any "edge" claim on a one-sided price harder to evaluate.
The break-even calculator takes an optional second price and reports the real overround.