Implied probability and the vig are the two foundational concepts that every sports bettor needs to understand. Miss either one and you'll consistently make bets that seem smart but aren't.
Implied Probability: What Every Price Means
Every betting odds price converts to an implied probability — the market's assessment of how likely that outcome is.
Positive odds (underdogs): Implied probability = 100 / (odds + 100) +150 → 100/250 = 40%
Negative odds (favorites): Implied probability = |odds| / (|odds| + 100) -200 → 200/300 = 66.7%
This probability is what the sportsbook is pricing the outcome at. If you believe the true probability is higher, you have positive expected value. If lower, negative expected value.
The Vig: Where the Math Gets Complicated
In a fair two-outcome market (no house edge), both sides would sum to exactly 100%. A -110/-110 market doesn't sum to 100% — it sums to 104.76%.
-110 implied probability: 52.38% -110 implied probability: 52.38% Total: 104.76%
The excess 4.76% is the vig — the sportsbook's guaranteed profit on balanced action.
No-Vig: The True Implied Probability
To find the true implied probability (stripped of the vig), divide each side's implied probability by the total:
52.38 / 1.0476 = 50.0% each (on a balanced -110/-110 market)
On an asymmetric market like -130/+110: -130: 56.52% implied +110: 47.62% implied Total: 104.14%
No-vig: 56.52/1.0414 = 54.27%; 47.62/1.0414 = 45.73%
The no-vig price is the market's honest estimate of true probability, without the house cut.
Using This to Find Value
If you can bet the +110 side and believe the true probability is above 47.62%, you have positive EV. The no-vig calculation reveals exactly what probability threshold you need to exceed.
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