Implied Probability Explained: How to Convert Odds to Win Percentage

What is Implied Probability?

Implied probability is the win percentage that betting odds suggest. When a sportsbook sets odds at -150, they're implying a certain probability that outcome will happen. Understanding this conversion is fundamental to finding value bets.

The concept is simple: every set of odds can be translated into a percentage. -200 implies about 67%. +200 implies about 33%. Knowing these conversions instantly tells you what the market thinks about each outcome.

Converting American Odds to Probability

American odds come in two flavors: negative (favorites) and positive (underdogs). Each uses a different formula.

Negative Odds (Favorites)

Implied Probability = Odds / (Odds + 100)

Example: -150 odds

150 / (150 + 100) = 150 / 250 = 0.60 or 60%

The sportsbook is implying this outcome has a 60% chance of happening.

Positive Odds (Underdogs)

Implied Probability = 100 / (Odds + 100)

Example: +200 odds

100 / (200 + 100) = 100 / 300 = 0.333 or 33.3%

The sportsbook is implying this outcome has a 33.3% chance of happening.

Quick Reference Table

Or skip the math and use our odds converter for instant conversions.

Converting Decimal and Fractional Odds

Decimal Odds

Decimal odds are the simplest to convert:

Implied Probability = 1 / Decimal Odds

Example: 1.80 decimal odds

1 / 1.80 = 0.556 or 55.6%

Fractional Odds

Implied Probability = Denominator / (Numerator + Denominator)

Example: 5/2 fractional odds

2 / (5 + 2) = 2 / 7 = 0.286 or 28.6%

The Problem: Implied Probabilities Add Up to More Than 100%

Here's where it gets interesting. Take a standard spread bet:

• Team A: -110 (52.4%)
• Team B: -110 (52.4%)

Total: 104.8%

But wait. The actual probabilities must add up to exactly 100% since one team will cover. The extra 4.8% is the sportsbook's vig.

This is why implied probability alone isn't enough. You need to remove the vig to find the true probability.

Calculating True (No-Vig) Probability

To find what the odds would be without the vig, divide each implied probability by the total:

True Probability = Implied Probability / Total Implied Probability

Example: -110/-110 market (52.4% + 52.4% = 104.8%)

Team A True Prob = 52.4% / 104.8% = 50%
Team B True Prob = 52.4% / 104.8% = 50%

Now they add up to 100%, which reflects the actual market assessment.

Use our no-vig calculator to instantly devig any line.

Why Implied Probability Matters for Betting

Understanding implied probability lets you identify value. Here's the process:

1. Convert the odds to implied probability
2. Form your own estimate of the true probability
3. Compare the two. If your estimate is higher than implied, you have potential value

Example:

The Chiefs are +150 to win (implied 40%). You analyze the matchup and believe they have a 50% chance. That 10-point gap suggests a +EV bet.

Of course, being right about your own estimates is the hard part. This is why many bettors use sharp market prices (like Pinnacle) as their "true probability" baseline and look for softer books offering better odds.

Implied Probability Across Different Markets

Different bet types have different typical vig levels, which affects how you interpret implied probabilities:

When implied probabilities add up to 130%, half of that "probability" is vig. You need a much larger edge to overcome high-vig markets.

Practical Applications

Comparing Odds Across Sportsbooks

When two books offer different odds on the same outcome:

• Book A: Chiefs +145 (40.8% implied)
• Book B: Chiefs +160 (38.5% implied)

Book B is giving you 2.3 percentage points less implied probability for the same outcome. That's better value because they're implying the Chiefs are less likely to win, which means higher payout if they do.

Evaluating Parlay Legs

Before adding a leg to your parlay, convert it to probability and ask: "Do I really think this has a better chance than X%?"

Adding a -300 favorite (75% implied) feels safe, but you're laying 3-to-1 odds. One loss in four wipes out your profit.

Assessing Prop Bet Value

Player props often have high vig. An "over 24.5 points" at -130 implies 56.5%. But if the total implied probability is 115%, the true probability is only about 49% (56.5/115).

You need to believe the over has better than 49% chance, not 56.5%, to have value.

Common Mistakes

Confusing Implied with True Probability

-110 implies 52.4%, but the true probability in a fair market is 50%. Betting every -110 line as if you have a 52.4% chance to win is exactly why the house wins.

Ignoring Vig on High-Juice Lines

A -200 favorite implies 66.7%, but if the underdog is +160 (38.5%), the total is 105.2%. The true probability of the favorite is closer to 63.4%. That three-point difference matters.

Using Implied Probability as Your Estimate

Implied probability tells you what the market thinks. It doesn't tell you what's actually going to happen. Using it as your personal estimate means you'll never find value because you're always agreeing with the market.

Key Takeaways

• Implied probability converts odds to a percentage the market suggests
• Negative odds: Odds / (Odds + 100)
• Positive odds: 100 / (Odds + 100)
• Probabilities add up to more than 100% because of vig
• To find true probability, divide by the total and normalize to 100%
• Value exists when true probability exceeds implied probability
• Use a no-vig calculator to quickly strip the margin from any line