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A sportsbook's two prices always imply more than 100% combined — the excess is the vig, the book's margin. De-vigging strips it out proportionally, leaving the market's fair probabilities and the fair odds each side would carry with no margin at all. It is arithmetic on the prices, not a prediction about the game.
Implies 60.0% — vig included
Implies 43.5% — vig included
Side A fair probability
57.98%
Fair odds: -138 American · 1.725 decimal
Side B fair probability
42.02%
Fair odds: +138 American · 2.380 decimal
Overround (vig)
3.48%
Sum of both implied probabilities, minus 100%
The two fair probabilities always sum to exactly 100% — that is the definition of removing the vig, not a prediction about the game.
Each American price converts to a vig-inclusive implied probability. Because the book charges a margin, the two sides sum to more than 100%. The proportional (multiplicative) method scales both back onto 100%:
Example: −150 / +130 implies 60.0% + 43.5% = 103.5%. Normalizing gives fair probabilities of 58.0% / 42.0% — fair odds of −138 / +138. This is the same de-vig Blitzen's own edge math uses everywhere (client and server run the identical formula), because measuring anything against a vig-inclusive price overstates it by roughly half the book's margin.
The proportional method is the standard baseline, but it is an assumption, not a law — it spreads the margin in proportion to the prices. Fair prices are the honest yardstick for line shopping and for closing-line-value analysis: comparing the number you got against the market's final fair number.
More free tools
These calculators run the exact helpers the Blitzen terminal uses on every board. See them applied to real markets — and how we grade everything against the close.