Every set of betting odds has a hidden number behind it: the implied probability. It’s the win percentage the sportsbook is pricing into the line. Understanding implied probability is the first step to finding value bets.
What is Implied Probability?
Implied probability is the likelihood of an outcome happening, as suggested by the betting odds. It answers the question: “According to this line, how often does this bet need to win to break even?”
-200 odds imply a 66.7% chance of winning
+150 odds imply a 40.0% chance of winning
-110 odds imply a 52.4% chance of winning
If you believe the true probability is higher than the implied probability, the bet has value.
How to Calculate It
From American Odds
Negative odds (favorites):
Implied Probability = |odds| / (|odds| + 100)
Example: -200 → 200 / (200 + 100) = 200/300 = 66.7%
Positive odds (underdogs):
Implied Probability = 100 / (odds + 100)
Example: +150 → 100 / (150 + 100) = 100/250 = 40.0%
From Decimal Odds
Implied Probability = 1 / decimal odds
Example: 2.50 → 1 / 2.50 = 40.0%
This is why decimal odds are great for quick mental math.
Try the implied-probability-calculator→
The Overround: Where the House Edge Lives
Here’s the catch: if you add up the implied probabilities from both sides of a two-way market, they’ll total more than 100%.
Example: NFL Moneyline
| Side | Odds | Implied Probability |
|---|---|---|
| Chiefs | -200 | 66.7% |
| Raiders | +170 | 37.0% |
| Total | 103.7% |
That extra 3.7% above 100% is the overround (also called vig, juice, or margin). It’s how the sportsbook guarantees profit regardless of the outcome.
The overround means the odds-implied probabilities are inflated. Neither side is priced at fair value — both are slightly overstated.
Fair Probability vs. Implied Probability
To find the “true” probability the market is pricing, you need to remove the overround. This is called de-vigging or calculating no-vig fair odds.
Using the example above (103.7% total):
| Side | Implied | Fair (De-vigged) |
|---|---|---|
| Chiefs | 66.7% | 64.3% |
| Raiders | 37.0% | 35.7% |
| Total | 103.7% | 100.0% |
The fair probability is what matters for expected value calculations. Compare your estimated win probability against the fair probability, not the raw implied probability.
Why Implied Probability Matters
Value identification: If you think a team has a 50% chance of winning but the implied probability is only 40%, that’s a +EV bet.
Quick gut-checks: Before placing any bet, convert the odds to a probability. Does the number feel right? If a team is implied at 80% to win and you think it should be 60%, the other side has massive value.
Comparing across books: Different sportsbooks have different overrounds. Comparing implied probabilities reveals which book is offering the best value.
Parlay math: Multiply individual implied probabilities to see the true likelihood of hitting a parlay. A 3-leg parlay of 50% events has a 12.5% chance of hitting.
Key Takeaways
Implied probability converts odds into the break-even win percentage
The sum of implied probabilities always exceeds 100% — the excess is the sportsbook’s edge
De-vig the odds to find the true fair probability
Compare your estimated probability to the implied probability to find value
