No-Vig Fair Odds Calculator

What Is Vig (and What Does “No-Vig” Mean)?

Every sportsbook and prediction market builds a margin into its prices. That margin goes by several names — vigorish (vig), juice, overround, house edge — but the mechanics are always the same: the prices you see imply a total probability that exceeds 100%. The excess is the operator’s built-in cut.

Here’s how it works concretely. Take a standard point spread priced at -110 on both sides. Converting -110 to implied probability:

• Side A: -110 → 110 / (110 + 100) = 52.38%
• Side B: -110 → 110 / (110 + 100) = 52.38%
• Sum: 52.38% + 52.38% = 104.76%

The probability of all outcomes in a two-way market should sum to exactly 100%. The extra 4.76% is the vig — the bookmaker’s theoretical margin, collected regardless of which side wins.

The same structure appears in prediction markets. If a Kalshi contract shows YES at 52¢ and NO at 52¢, you’re paying $1.04 total to cover both sides of a contract that pays out $1.00. That 4¢ excess is the same concept as the 4.76% overround on -110/-110 — just expressed in cents rather than percentage points.

“No vig” means that excess has been removed. A no-vig line strips the operator’s margin and rescales the probabilities back to 100%, revealing the market’s actual implied probability for each outcome. This is the number you should compare against your own estimate when deciding whether a trade has edge.

How the No-Vig Fair Odds Calculation Works

The standard method — proportional (multiplicative) devigging — works in three steps:

Step 1: Convert to Implied Probability

Regardless of the starting format, convert each outcome’s odds to implied probability:

• American (negative): |odds| / (|odds| + 100)
• American (positive): 100 / (odds + 100)
• Decimal: 1 / decimal odds
• Prediction market price: The contract price itself (e.g., 62¢ = 0.62)

Step 2: Sum and Identify the Overround

Add all implied probabilities. The amount over 1.00 (or 100%) is the overround.

Step 3: Normalize

Divide each side’s implied probability by the total. The results are the fair (no-vig) probabilities, which sum to exactly 100%.

Worked Example: Two-Way Market

A moneyline is listed at -150 / +130.

Overround: 3.48%

Normalize:

• Favorite fair probability: 60.00 / 103.48 = 57.98% → fair odds -138
• Underdog fair probability: 43.48 / 103.48 = 42.02% → fair odds +138

The raw -150 line implied 60% — but after removing the vig, the market’s actual estimate of the favorite is 57.98%. That 2.02 percentage point difference is entirely margin.

Worked Example: Three-Way Market

A soccer match is priced: Home +135 / Draw +240 / Away +210.

Overround: 4.22%

Normalize:

• Home: 42.55 / 104.22 = 40.83%
• Draw: 29.41 / 104.22 = 28.22%
• Away: 32.26 / 104.22 = 30.95%

Three-way markets tend to carry higher overround (commonly 4–8%) because the book has three surfaces to embed margin in. The normalization step works identically regardless of the number of outcomes.

When and Why Traders Devig

Removing the vig isn’t an academic exercise. Traders devig lines for three concrete reasons:

1. Comparing a sharp book’s prices to a soft book’s. Reduced-juice sportsbooks (e.g., Pinnacle) carry less margin, so their devigged lines are considered a closer proxy for true probability. If Pinnacle’s devigged line on an NFL game implies 54% for the home team and a recreational book prices the same side at +105 (implied 48.78%, which devigs even lower), the gap may represent genuine value — not just different margin structures.

2. Estimating “true” probability from prediction market prices. On Kalshi or Polymarket, the YES/NO prices include spread and fee effects. Devigging the best bid/ask midpoint gives you a cleaner estimate of the market’s consensus probability — useful for comparing against your own model or a second platform’s price.

3. Spotting stale lines across platforms. When two sportsbooks or two prediction markets disagree on devigged fair odds by more than a few percentage points, one line may be stale. This is the foundation of cross-platform comparison — and it’s where devigging connects directly to arbitrage. The wider the gap after vig removal, the more likely one side hasn’t adjusted to new information.

In all three cases, the point is the same: raw odds are contaminated by margin. Devigging isolates the market’s probability signal from the operator’s cut.

Worked Examples with Real-World Numbers

Example 1: Kalshi Binary Contract

A Kalshi contract on “Will the Fed cut rates at the June meeting?” shows:

Overround: 2.00% (typical for active Kalshi contracts where the spread is tight)

Fair no-vig probabilities:

• YES: 38.00 / 102.00 = 37.25% → fair price 37.3¢
• NO: 64.00 / 102.00 = 62.75% → fair price 62.7¢

If you believe the true probability of a rate cut is 42%, you have roughly 4.75 percentage points of edge on the YES side (42% – 37.25%). That’s real edge — not just the vig creating an illusion.

Example 2: Sports Moneyline (Two-Way)

An NBA moneyline: Celtics -220 / Mavericks +180.

Overround: 4.46%

Fair no-vig:

• Celtics: 68.75 / 104.46 = 65.82% → fair odds -193
• Mavericks: 35.71 / 104.46 = 34.19% → fair odds +193

The raw -220 implied the Celtics at 68.75%. After devigging: 65.82%. If a second sportsbook offers the Celtics at -190 (implied 65.52%), that line is actually below the devigged fair price from this book — that’s how you spot value using no-vig odds as a benchmark.

Example 3: Soccer Three-Way

Premier League match: Liverpool -125 / Draw +280 / Arsenal +310.

Overround: 6.27% — higher than the two-way examples, as expected for a three-way market.

Fair no-vig:

• Liverpool: 55.56 / 106.27 = 52.28%
• Draw: 26.32 / 106.27 = 24.77%
• Arsenal: 24.39 / 106.27 = 22.95%

Liverpool’s raw implied probability was 55.56% — devigged, it’s 52.28%. That 3.28 percentage point gap is entirely bookmaker margin.

Common Mistakes When Devigging

Treating asymmetric markets the same as balanced ones. At -110/-110, the vig is distributed roughly evenly. At -500/+380, it’s not. Proportional devigging assumes the book distributes margin proportionally across all outcomes. In reality, sportsbooks often shade the favorite side more heavily (because that’s where recreational volume concentrates). For heavily lopsided lines, be aware that the devigged result is an approximation — the true fair odds may differ slightly depending on how the book allocated its margin.

Assuming proportional devigging is always the correct method. Proportional (multiplicative) devigging is the most common approach and works well for balanced-to-moderately-skewed markets. But it makes a specific assumption: that the book adds vig to each outcome in proportion to its probability. If the book instead shades one side more than the other (common on recreational-heavy props), the proportional method can over- or under-correct on each side. This doesn’t mean the method is wrong — it means you should treat the output as an estimate, not a ground truth.

Confusing prediction market fees with baked-in vig. On sportsbooks, the vig is embedded in the odds themselves — it’s invisible unless you do the math. On Kalshi, there’s an explicit fee formula — 0.07 × contracts × p × (1 − p), rounded up to the next cent — charged on top of the trade. These are structurally different. Devigging a Kalshi price removes the spread-based overround, but the explicit fee is a separate cost layer. You need to account for both. See the Fees Compared calculator for the full picture.

Using last-trade price as a current quote. On illiquid prediction markets, the last-trade price can be hours or days old. Devigging a stale price produces a stale fair probability. Always use the current best bid and ask — or at minimum the midpoint — rather than the last executed trade when devigging prediction market contracts.

Proportional vs. Other Devigging Methods

This calculator uses proportional (multiplicative) devigging — the most widely used method. It divides each implied probability by the total, distributing the margin removal proportionally. For markets with moderate overround (2–6%) and outcomes that aren’t extremely lopsided, it produces reliable results.

Two alternative methods exist for edge cases. Shin’s method models the overround as partly driven by informed bettors, producing slightly different fair probabilities for heavy favorites. It’s more commonly used in horse racing markets with many runners and wide overrounds. The power method adjusts probabilities using an exponent, which can better handle markets where the book’s margin isn’t proportionally distributed. Both methods converge toward the proportional result when the overround is small and outcomes are relatively balanced.

For most two-way and three-way markets at standard overround levels, the practical difference between methods is small — often under 0.5 percentage points. The proportional method is the right default. If you’re devigging heavily skewed props or markets with 15%+ overround, be aware that alternative methods may produce meaningfully different results.

No-Vig Odds in Prediction Markets

Devigging originated in sports betting, but the concept applies directly to prediction markets — with a structural twist.

On a sportsbook, the vig is invisible. It’s baked into the odds: -110/-110 looks like a fair coin flip, but it isn’t. The operator’s margin hides inside the price itself, and the only way to see it is to devig.

On prediction markets like Kalshi and Polymarket, the margin comes from two sources: the spread (the gap between best bid and best ask) and explicit fees charged per trade. A Kalshi contract might show a best bid of 47¢ and a best ask of 53¢. The midpoint is 50¢, but you’ll pay 53¢ to buy YES — and the fee formula adds cost on top. This means prediction market “vig” is partly visible (the fee) and partly embedded (the spread).

When you devig prediction market prices, you’re removing the spread-based overround — the same normalization step as in sports. But you still need to account for the platform’s explicit fees separately. A no-vig probability of 50% on a Kalshi contract still costs more than 50¢ to trade because of the 0.07 × contracts × p × (1 − p) taker fee, rounded up per trade.

This is why ChanceMetrics separates the tools: the no-vig calculator isolates the market’s implied probability; the Fees Compared calculator quantifies the platform cost; and the EV Calculator combines both into a net expected value for a specific trade. The three work together — devig first, then check fees, then evaluate edge.

For a full comparison of how fee structures differ between Kalshi and Polymarket, see Kalshi vs Polymarket.

Overround Calculator: Measure the Bookmaker’s Edge

The overround is the sum of all implied probabilities across a market’s outcomes, minus 100%. On a standard -110/-110 spread, each side implies 52.38% — the overround is 4.76%. That excess is the bookmaker’s guaranteed theoretical edge, regardless of which side wins.

Overround compounds in parlays and multi-leg markets, which is why multi-leg bets are structurally expensive even when each individual leg looks fair. This calculator shows the overround for any 2-way or 3-way market — a useful gut check before placing any wager.

For prediction markets like Kalshi, where the contract prices (e.g., 63¢ YES / 39¢ NO) sum to more than 100¢, the overround is the excess over $1.00. The same math applies. See how that interacts with explicit platform fees in the Fees Compared tool.

Frequently Asked Questions

Common questions about vig, devig, overround, and no-vig fair odds.