When you look at a betting line, you are not seeing the true probability of an event. You are seeing the probability plus the bookmaker’s fee, known as the “vig,” “vigorish,” or “margin.”
For example, if two NFL teams are perfectly matched, the fair odds should be +100 (2.00) for each side. However, sportsbooks typically list both sides at -110 (1.91). That difference is the cost of placing the bet. Our No-Vig Calculator strips away this fee to reveal the Fair Odds and the market-implied True Win Probability — what the line suggests the real chance is, without the bookmaker’s cut.
This is the first step in understanding what the market believes about a game. If your own analysis disagrees with the no-vig probability, you may have found an edge.
No-Vig Calculator
Fair OddsPower: raises each prob to a power k such that they sum to 1. Better for lopsided lines.
Additive: subtracts equal margin from each side. Simplest but least accurate for asymmetric markets.
| Side 1 | Side 2 | |
|---|---|---|
| Fair Probability | — | — |
| Fair Odds (US) | — | — |
| Fair Odds (Decimal) | — | — |
| Breakeven (with vig) | — | — |
How to Use the No-Vig Calculator
This tool removes the bookmaker’s margin from a 2-way line to show the underlying market probabilities.
- Select Market Type:
- Spread / Handicap: For betting on the margin (e.g., Chiefs -3.5).
- Over / Under: For betting on the total (e.g., Total 220.5).
- Choose Odds Format: Click the format toggle to switch between American (-110) and Decimal (1.91).
- Enter Odds for Both Sides: You must input odds for both outcomes. The vig is derived from the gap between the two lines.
- Example: Chiefs -120 and Ravens +100.
- Choose Devig Method:
- Multiplicative (default): Divides each implied probability by the total. Most widely used.
- Power: Raises each probability to a calibrated exponent. Better for lopsided lines.
- Additive: Subtracts equal margin from each side. Simplest but least accurate for asymmetric markets.
- Read the Results:
- Fair Probability: The market-implied chance of each side winning, with the vig removed.
- Fair Odds: Shown in both American and Decimal formats — the price a zero-margin bookmaker would offer.
- Breakeven Win Rate: The win rate you need at the original (vigged) odds just to break even.
- Vig %: The total margin the bookmaker is charging on this market.
- (Optional) Check Your Edge: Enter your own estimated true probability. The calculator compares it with the market’s no-vig probability and tells you whether you see value.
Related Tools: Once you have identified a +EV bet, use the Kelly Criterion Calculator to determine optimal stake size. For 3-way markets (football 1X2), use the Margin Calculator instead.
The Formulas
All devig methods start with converting odds to implied probabilities.
American to Implied:
For negative odds (e.g., -125): Implied = |odds| / (|odds| + 100).
For positive odds (e.g., +105): Implied = 100 / (odds + 100).
Decimal to Implied: Implied = 1 / Decimal Odds.
The sum of both implied probabilities will exceed 100% — the excess is the vig.
Multiplicative Devig (Default)
Fair Prob (Side A) = Implied A / (Implied A + Implied B)
This proportionally scales each side so they sum to 100%. It is the most common method and works well for nearly symmetric lines.
Power Devig
Find exponent k such that: Implied Ak + Implied Bk = 1
Then: Fair Prob (Side A) = Implied Ak
This method distributes the vig unevenly — the favourite absorbs a slightly larger share. Many sharp bettors prefer it for lopsided lines because it better reflects how bookmakers typically build their margin.
Additive Devig
Excess = (Implied A + Implied B − 1) / 2
Fair Prob (Side A) = Implied A − Excess
Subtracts equal margin from both sides. Simple but can produce inaccurate results when the line is heavily skewed.
Vig Calculation
Vig% = (1 − 1 / (Implied A + Implied B)) × 100
Important: Fair Odds ≠ True Probability
The no-vig probability reflects the market’s consensus, not an objective truth. It represents what the combined betting action and the bookmaker’s model imply about the game — with the house edge stripped out.
If you believe a team’s true chance differs from the market consensus, that is where a potential edge exists. But the market includes sharp money, bookmaker models, injury reports, and public opinion — so disagreeing with it requires strong conviction backed by your own analysis.
Real-World Examples
Example 1: The Standard Line (-110 / -110)
Most NFL spreads open with both sides at -110.
- Implied Probability (with vig): 52.38% per side.
- Total Market: 104.76%. The extra 4.76% is the vig.
- No-Vig Fair Probability: 50.00% / 50.00%.
- Fair Odds: +100 / +100 (2.00 / 2.00 Decimal).
- Takeaway: You must win 52.38% of your -110 bets just to break even. The market sees the game as a coin flip.
Example 2: A Lopsided Line (-125 / +105)
- Favourite (-125): Implied = 55.56%. After Multiplicative devig: Fair Prob = 53.26%. Fair Odds: -114 (1.88 Decimal).
- Underdog (+105): Implied = 48.78%. After devig: Fair Prob = 46.74%. Fair Odds: +114 (2.14 Decimal).
- Takeaway: The market’s true view is ~53/47. The underdog at +105 is not great value — the no-vig fair price is +114. To have an edge on the underdog, you would need to believe their true chance is above 46.74%.
Frequently Asked Questions (FAQ)
What is “Push Logic” in 2-way markets?
In Spread and Total markets, an exact-number result is a Push (money returned). The no-vig calculation ignores this and normalizes Side A + Side B = 100%. The result shows: “Given a decisive outcome (no push), what is the probability of each side winning?”
Why do I need to enter odds for both sides?
The vig cannot be calculated from one side alone. It is the gap between the two lines that reveals the bookmaker’s margin. The wider the gap, the higher the fee.
What are “Fair Odds”?
Fair Odds (or True Odds, No-Vig Odds) are the break-even price of a bet with zero house edge. They represent the market’s consensus probability converted back into odds format. If you can find a sportsbook offering better than the Fair Odds, the market implies you have a positive expected value (+EV) bet.
Which devig method should I use?
Multiplicative is the safest default and works well for nearly symmetric lines (e.g., -110/-110). Power is generally preferred by sharps for lopsided lines because it better reflects how bookmakers distribute vig. Additive is the simplest but least accurate for skewed markets. When in doubt, use Multiplicative and check against Power for heavily favoured sides.
Does the “Your Edge” check tell me whether to bet?
It tells you whether your estimated probability disagrees with the market. If your estimate is higher than the no-vig fair probability for a side, the market implies that side is underpriced from your perspective. Whether to act on that depends on your confidence in your own estimate and your bankroll management strategy.