Implied Probability Calculator
Convert betting odds to win probability and identify value
How to Use This Calculator
This calculator has two modes:
Single Odds Mode:
- Enter American odds (e.g., -110 or +150)
- Click "Calculate" to see the implied win probability
Compare Mode (Find Vig):
- Enter both teams' odds from a game
- Click "Calculate" to see implied probabilities, true probabilities, and bookmaker edge
What is Implied Probability?
Implied probability is the conversion of betting odds into a percentage that represents the likelihood of an outcome according to the bookmaker.
Example:
Chiefs at -150 odds to win
Implied Probability = 150 / (150 + 100) = 60%
This means the bookmaker is pricing the Chiefs as if they have a 60% chance to win.
Understanding implied probability helps you identify value bets - situations where you believe the true probability is higher than what the odds suggest.
What is the Vig (Bookmaker Edge)?
The "vig" (short for vigorish) or "juice" is the commission bookmakers charge. It's built into the odds and represents their profit margin.
Example of Vig:
Team A: -110 odds = 52.38% implied probability
Team B: -110 odds = 52.38% implied probability
Total: 52.38% + 52.38% = 104.76%
Vig: 4.76%
In a fair market, probabilities would total 100%. The extra 4.76% is the bookmaker's edge - what they keep regardless of outcome.
Lower vig means better odds for bettors. Comparing vig across sportsbooks helps you find the best value.
How to Find Value Bets
A value bet exists when you believe the true probability of an outcome is higher than the implied probability from the odds.
Value Bet Example:
Bookmaker odds: Chiefs +200 (33.33% implied probability)
Your analysis: Chiefs have a 40% chance to win
This is a VALUE BET! 40% > 33.33%
You believe the Chiefs are more likely to win than the odds suggest, giving you a mathematical edge.
Pro Strategy:
- Calculate implied probability from bookmaker odds
- Estimate the true probability using your analysis
- Bet when true probability > implied probability
- The bigger the gap, the more value in the bet
Quick Reference: Probability to American Odds
| Implied Probability | American Odds | Decimal Odds |
|---|---|---|
| 90% | -900 | 1.11 |
| 75% | -300 | 1.33 |
| 66.67% | -200 | 1.50 |
| 52.38% | -110 | 1.91 |
| 50% | +100 | 2.00 |
| 40% | +150 | 2.50 |
| 33.33% | +200 | 3.00 |
| 25% | +300 | 4.00 |
| 10% | +900 | 10.00 |
Frequently Asked Questions
Is implied probability the actual probability?
No. Implied probability includes the bookmaker's vig. The true probability is always slightly lower. Use the "Compare" mode to see true probabilities after removing vig.
What's a good vig percentage?
Standard NFL/NBA lines typically have 4-5% vig (like -110/-110). Lower is better for bettors. Some sharp books offer reduced vig as low as 2-3%. Player props and parlays often have much higher vig (10%+).
How do I calculate value bet size?
Many pros use the Kelly Criterion: Bet% = (True Probability × Decimal Odds - 1) / (Decimal Odds - 1). However, most bettors use fractional Kelly (1/4 or 1/2) to reduce variance.