No-Vig Odds Explained: How to Calculate True Probabilities

What Is Vig (Vigorish)?

Vig (also called juice, margin, or overround) is the bookmaker's built-in profit margin on every market they offer. It's the reason sportsbooks are profitable businesses.

In a fair market (like a coin flip), both sides would be priced at +100 (decimal 2.00), implying 50% probability each. The total implied probability would be exactly 100%.

But sportsbooks don't offer fair markets. Instead, they price both sides at around -110 (decimal 1.91), implying 52.4% probability each. The total: 104.8%. That extra 4.8% is the vig, which is the sportsbook's edge.

Why Removing the Vig Matters

If you're trying to find value bets or calculate expected value, you need the true probability of an outcome, not the inflated implied probability that includes the bookmaker's margin.

No-vig odds give you:

• True fair probabilities, showing what the market actually thinks will happen
• A baseline for finding value by comparing no-vig odds against other books to spot mispricing
• Accurate EV calculations since your expected value calculations are only as good as your probability estimates
• Understanding of the real edge and how much margin the book is actually taking

How to Calculate Implied Probability

Before removing the vig, you need to convert odds to implied probability.

From Decimal Odds

Implied Probability = 1 / Decimal Odds

Example: Odds of 1.91 → 1 / 1.91 = 52.36%

From American Odds

For negative odds (favorites):

Implied Probability = |American Odds| / (|American Odds| + 100)

Example: -150 → 150 / (150 + 100) = 150 / 250 = 60%

For positive odds (underdogs):

Implied Probability = 100 / (American Odds + 100)

Example: +200 → 100 / (200 + 100) = 100 / 300 = 33.33%

The Overround

When you add up the implied probabilities for all outcomes in a market, the total will exceed 100%. That excess is the overround, which is the vig expressed as a percentage.

Example: NFL Moneyline

• Team A: -180 (implied: 64.29%)
• Team B: +155 (implied: 39.22%)
• Total: 103.51%
• Overround: 3.51%

The book is charging a 3.51% margin on this market. The true probabilities must add to 100%, so both sides are inflated.

Devigging Methods

There are several methods to remove the vig and extract true probabilities. Each makes different assumptions about how the bookmaker distributes their margin.

Method 1: Multiplicative (Proportional)

The most common and simplest method. It assumes the vig is distributed proportionally across all outcomes.

True Probability = Implied Probability / Total Implied Probability

Using our NFL example:

• Team A true: 64.29% / 103.51% = 62.11%
• Team B true: 39.22% / 103.51% = 37.89%
• Total: 100.00%

Pros: Simple, widely used, works well for two-way markets. Cons: Tends to overestimate the probability of favorites in markets with large vig.

Method 2: Additive

Distributes the vig equally across all outcomes rather than proportionally.

Vig per side = (Total Implied - 1) / Number of Outcomes
True Probability = Implied Probability - Vig per side

Using our NFL example:

• Vig per side: (1.0351 - 1) / 2 = 0.01755
• Team A true: 64.29% - 1.755% = 62.54%
• Team B true: 39.22% - 1.755% = 37.46%

Pros: Simple. Cons: Unrealistic for markets with uneven odds because a heavy favorite and a longshot shouldn't have the same absolute vig removed.

Method 3: Power Method

Uses exponents to remove the vig in a way that accounts for the asymmetry between favorites and underdogs. The bookmaker's margin is removed by finding an exponent k such that the adjusted probabilities sum to 1.

This method generally produces results between multiplicative and Shin, and is considered a good all-around choice.

Pros: Handles asymmetric markets well. Cons: Requires iterative calculation, not practical by hand.

Method 4: Shin Method

Developed by Hyun Song Shin, this method assumes the vig exists partly because some bettors have insider information. It distributes more of the margin to longshots (where insider information has the most impact).

The Shin method is widely regarded as the most theoretically sound approach for removing vig from sports betting markets.

Pros: Most accurate for markets with potential information asymmetry, favored by academics and sharp bettors. Cons: Complex calculation, requires numerical solving.

Which Method Should You Use?

For most bettors, multiplicative is good enough. If you want more accuracy, especially on markets with heavy favorites or player props, use Shin or Power.

Practical Application: Finding Value

Once you have no-vig probabilities from a sharp book, you can compare them against lines at other sportsbooks to find value.

Step-by-Step

1. Take the sharp line. For example, Pinnacle has Team A at -170 / Team B at +150
2. Remove the vig. Using multiplicative: Team A true probability = 61.5%, Team B = 38.5%
3. Convert to fair odds. Team A fair: 1.626 (-160), Team B fair: 2.597 (+160)
4. Compare against other books. If DraftKings has Team B at +175 (implied 36.4%), but the true probability is 38.5%, you're getting odds that imply a lower probability than reality
5. Calculate EV. EV = (0.385 x 1.75) - (0.615 x 1) = 0.674 - 0.615 = +5.9%

That's a +EV bet with nearly 6% expected edge.

Understanding Market Vig Levels

Different markets have different levels of vig, which affects how much value you can find:

Lower vig markets are more efficient but offer thinner edges. Higher vig markets have more room for mispricing but require a larger edge to be profitable.

Common Mistakes

Using Vig-Inclusive Odds as True Odds

If you calculate EV using the implied probability from a sportsbook line without removing the vig, you'll systematically underestimate your edge (or think you have an edge when you don't).

Devigging Recreational Books

Only devig sharp books. Recreational books (DraftKings, FanDuel, BetMGM) shade their lines based on public action, so their odds don't reflect true probabilities even after removing the vig. Use Pinnacle or other sharp books as your source of truth.

Ignoring Vig When Comparing Odds

Two books might offer the same headline odds on a bet, but if one has 3% vig and the other has 6%, the lower-vig book is giving you a better deal overall.

Key Takeaways

• Vig is the bookmaker's margin and it inflates implied probabilities above 100%
• No-vig odds reveal true probabilities, which is essential for finding value bets
• Multiplicative devigging works well for most two-way markets
• Shin method is the most accurate for markets with information asymmetry
• Only devig sharp books because recreational book lines don't reflect true probabilities
• Use a calculator since manual devigging is tedious and error-prone