The Vig in Sports Betting Explained — What It Is and How to Remove It

Every sportsbook builds a hidden commission into the odds you see. That commission is called the vig — short for vigorish, also known as the juice — and understanding it is the single most important quantitative skill in sports betting. Without it, you cannot calculate expected value, you cannot identify mispriced lines, and you cannot compare a sportsbook's opinion to your own probability estimate or to an AI prediction model's output. This guide covers exactly what the vig is, how it works mechanically, the step-by-step formula to strip it out, and why the concept applies differently on prediction markets like Polymarket.

What the Vig Actually Is

When a sportsbook posts a standard NFL spread at -110 on both sides, both outcomes require a $110 wager to win $100. If the book takes exactly equal action on each side, it collects $220 in total wagers and pays out $210 to the winning side — keeping $10 regardless of which team covers. That guaranteed $10 margin is the vig.

The vig is not a fixed dollar amount. It is a percentage embedded in the odds structure. On a -110/-110 line, the implied probability of each side is 52.38% (calculated as 110 ÷ 210). Adding both sides together gives you 104.76% — not 100%. That extra 4.76 percentage points above certainty is the overround, and it represents the book's mathematical edge.

Think of it this way: the sportsbook is pricing the universe of outcomes as if there were a 104.76% chance that something happens. Since the actual probability of all outcomes must sum to exactly 100%, the difference between the overround and 100% is the house's built-in profit margin. Over millions of bets, that margin compounds into enormous revenue — and it is why sportsbooks are profitable businesses regardless of who wins on any given Sunday.

How Vig Varies Across Markets

Not all markets carry the same vig. Understanding where the vig is thinnest (and thickest) tells you where the book has invested the most effort in line accuracy and where softer lines might exist.

NFL and NBA sides and totals at sharp books like Pinnacle carry an overround of approximately 2–3%. These are the most efficient markets in sports because they handle the largest volume. The book invests heavily in accurate pricing because the liability is enormous.

NFL and NBA player props often carry 6–12% overround. Books price hundreds of individual props per game — passing yards, rushing yards, receiving yards, anytime touchdowns — and simply cannot invest the same modeling resources into each one. The higher vig is partly compensation for less precise pricing, which paradoxically means there is more edge available in props despite the higher commission. This is why player prop strategy is one of the most profitable niches for analytical bettors.

Parlays and teasers carry an implicit vig that compounds with each leg. A two-team parlay at true 3-to-1 odds might pay only 2.6-to-1, embedding a vig that far exceeds the vig on either individual leg. The compounding effect makes multi-leg parlays among the highest-margin products sportsbooks offer.

Futures markets — season win totals, championship outrights, MVP awards — carry overrounds that can exceed 20–40% because the book is pricing a large field of outcomes and padding each one. The further in advance a future is priced, the more vig it tends to carry.

How to Remove the Vig: Step-by-Step

Stripping the vig — also called de-vigging or calculating no-vig odds — gives you the sportsbook's "true" implied probability for each side, minus the commission. This is what the market actually believes, cleaned of the house's profit margin. Here is the standard method.

Example 1: A -110/-110 Line

Step 1 — Convert each side to implied probability. For American odds, the conversion formulas are:

• Negative odds: |odds| ÷ (|odds| + 100)
• Positive odds: 100 ÷ (odds + 100)

Side A at -110: 110 ÷ 210 = 0.5238 (52.38%) Side B at -110: 110 ÷ 210 = 0.5238 (52.38%)

Step 2 — Sum the implied probabilities: 52.38% + 52.38% = 104.76%. This total exceeding 100% confirms the vig is present.

Step 3 — Normalize each side back to 100% by dividing each implied probability by the total:

• Side A no-vig: 52.38% ÷ 104.76% = 50.00%
• Side B no-vig: 52.38% ÷ 104.76% = 50.00%

A -110/-110 line is a coin flip once you strip the vig. The sportsbook sees each side as equally likely and charges you 4.76% for the privilege of betting on it.

Example 2: A -150/+130 Line

Side A (favorite) at -150: 150 ÷ 250 = 60.00% Side B (underdog) at +130: 100 ÷ 230 = 43.48% Total: 103.48% (overround of 3.48%)

No-vig favorite: 60.00% ÷ 103.48% = 57.98% No-vig underdog: 43.48% ÷ 103.48% = 42.02%

The market's true opinion is that the favorite wins roughly 58% of the time. Now you have a clean number to compare against your own model or an ensemble prediction consensus — if your estimate says the favorite wins 63% of the time, you have identified a potential edge worth investigating.

Example 3: A Three-Way Market (Football 1X2)

Football (soccer) match result markets have three outcomes: home win, draw, away win. The same process applies with three probabilities instead of two.

Home at 1.80 decimal: 1 ÷ 1.80 = 55.56% Draw at 3.60 decimal: 1 ÷ 3.60 = 27.78% Away at 4.50 decimal: 1 ÷ 4.50 = 22.22% Total: 105.56%

No-vig home: 55.56% ÷ 105.56% = 52.63% No-vig draw: 27.78% ÷ 105.56% = 26.32% No-vig away: 22.22% ÷ 105.56% = 21.05%

These three probabilities now sum to exactly 100%, giving you the market's cleaned opinion on the match.

Does the Vig Apply on Polymarket?

This is a critical question for anyone who trades both sportsbooks and prediction markets. The short answer: Polymarket does not have a traditional vig, but it does have a spread.

Prediction markets like Polymarket and Kalshi operate on an order book model — there is no house setting the odds. Buyers and sellers determine the price through supply and demand, exactly like a stock exchange. A Polymarket contract priced at $0.58 implies a 58% probability. The complementary "No" contract trades at $0.42 (42%). In a perfectly liquid market, these sum to exactly 100% — no vig.

Polymarket charges a small fee on winning trades (approximately 2%), but this fee is applied after resolution, not embedded in the pricing the way a sportsbook's vig is. The odds you see are not inflated by a house margin.

However, thin markets create a bid-ask spread that functions similarly to a vig in practice. If the best "Yes" ask is $0.60 and the best "No" ask is $0.44, covering both sides costs $1.04 — a 4% effective spread. You are paying 4 cents of friction per share to guarantee an outcome. In liquid Polymarket sports contracts, this spread is typically tighter than the vig on recreational sportsbooks, which is one reason sharp bettors have been migrating to prediction markets.

The practical takeaway for cross-platform comparison: always de-vig the sportsbook number before comparing it to a Polymarket contract price. Otherwise you are comparing an inflated probability against a market-derived probability, and the sportsbook will appear more confident in its assessment than it actually is.

Why Removing the Vig Matters for AI Prediction Models

When you use model-derived probability estimates — whether from your own build or from an ensemble prediction network like Sportstensor — the comparison against the market only works if the market number is clean.

Consider this scenario: your model says a team has a 58% probability of winning. The sportsbook prices them at -150, which implies 60%. On the surface, it looks like the market disagrees with your model and the bet might not have value. But when you de-vig the -150/+130 line, the true market probability is 57.98%. Your model's 58% is almost identical to the market's assessment — there is no edge.

Now flip it: if your model says 63% and the de-vigged market says 58%, that is a 5-percentage-point disagreement. On a -150 moneyline, that gap represents genuine expected value. Over hundreds of bets, those gaps are where long-term profit comes from.

The de-vigging step is not optional. It is the foundation that every subsequent EV calculation, CLV comparison, and model validation step depends on.

Frequently Asked Questions

What is the average vig on an NFL game? At sharp sportsbooks like Pinnacle or Circa, the overround on NFL sides and totals is typically 2–3%. At recreational US books like DraftKings or FanDuel, the standard -110/-110 line carries a 4.76% overround. Player props often carry 6–12% depending on the book and the market.

Is a lower vig always better? For the bettor, yes — a lower vig means you are paying less commission per bet, so your break-even win rate is lower. However, the lowest-vig books (like Pinnacle) tend to have the sharpest lines, meaning there is less pricing inefficiency to exploit. Some bettors prefer slightly higher-vig recreational books because the lines are softer and the edge opportunities are larger despite the higher commission.

Can I calculate the vig in decimal odds? Yes. Convert each decimal price to implied probability using 1 ÷ odds, then follow the same normalization process. Decimal odds are actually easier to de-vig because the formula is the same regardless of whether the outcome is favored.

Does Polymarket have a vig? Not in the traditional sense. Polymarket uses an order book with no house edge baked into the pricing. However, the bid-ask spread in less liquid markets functions similarly to a vig in practice. See the detailed section above.

The Bottom Line

The vig is the tax you pay every time you bet at a sportsbook. Removing it reveals what the market actually believes, stripped of commission. That clean probability is the baseline you compare every model output, every AI prediction, and every gut feel against. If you are not de-vigging lines before evaluating them, you are doing expected value calculations with inflated inputs — and making worse decisions as a result. Learn the formula, apply it to every line you evaluate, and you will immediately see the betting market with clearer eyes.