Every set of betting odds contains a hidden number — the sportsbook's estimate of how likely an outcome is, expressed as a percentage. That number is called implied probability, and learning to see it is what turns casual bettors into strategic ones.
When the sportsbook posts odds of -150, they're telling you — in code — that they think this outcome has about a 60% chance of happening. When you can decode that and compare it to your own estimate, you can identify +EV bets.
How to calculate implied probability
-200 odds: 200 ÷ (200 + 100) = 200 ÷ 300 = 66.7%
-110 odds: 110 ÷ (110 + 100) = 110 ÷ 210 = 52.4%
+150 odds: 100 ÷ (150 + 100) = 100 ÷ 250 = 40.0%
+300 odds: 100 ÷ (300 + 100) = 100 ÷ 400 = 25.0%
The vig inflates implied probability
Here's something most beginners miss: if you add up the implied probabilities of both sides of a bet, they'll total more than 100%. That's the vig.
Team A: -110 → implied probability = 52.4%
Team B: -110 → implied probability = 52.4%
Total: 104.8%
That extra 4.8% above 100% is the sportsbook's margin. Both outcomes can't truly add up to more than 100% — the sportsbook is overcharging both sides.
The more lopsided a market, the bigger the vig tends to be in absolute terms. A market with -300/+250 has the vig baked deeper into the favorite's price.
Stripping the vig to find fair odds
To find the sportsbook's "true" view of the game, you can remove the vig. The simplest method is proportional de-vigging:
So a standard -110/-110 line is really a 50/50 game with 4.8% juice. Knowing this, you can compare your estimated probability to the fair probability (not the inflated implied probability) and find your true edge.
Using implied probability to find +EV bets
This is where it all comes together. The process is simple:
- Convert the odds to implied probability. The sportsbook says -130 → that implies 56.5%.
- Estimate the true probability. Your research says this team wins 62% of the time in this situation.
- Compare. Your estimate (62%) is higher than the implied probability (56.5%). The bet is +EV.
- Calculate the edge. 62% − 56.5% = 5.5%. That's a meaningful edge.
If your estimate were 54% instead? The bet would be -EV — even though you think the team is more likely to win than lose. The odds aren't offering enough value for the risk.
This is the mindset shift. You're not asking "will this team win?" You're asking "are the odds offering me better value than my probability estimate?" Those are two completely different questions.
The bottom line: Implied probability is the percentage chance of winning that's embedded in the odds. Compare it to your own probability estimate. If yours is higher, the bet is +EV. If it's lower, the bet is -EV — and you walk away. Use the +EV Calculator to do this instantly.
Run the numbers before you bet.
The BeginnerBets +EV Calculator shows you instantly whether a bet is worth placing — based on math, not gut feeling.
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