Vig Calculator: How to Calculate Vigorish From Any Odds Format (2026 Guide)
A vig calculator is a tool that reveals how much margin a sportsbook bakes into its odds—known as the "vig" or "overround"—by converting betting lines into implied probabilities, summing them, and expressing the result as a percentage. You can calculate vig from American, decimal, or fractional odds using a few simple formulas, or automate the process with an online vig calculator for any market in 2026.
What Is Vig, and Why Does It Matter?
Vigorish (or "vig") is the built-in margin that sportsbooks add to their odds to ensure they make a profit regardless of event outcome. Vig is also called the "overround" or "hold." For example, in a standard -110/-110 point spread, the sportsbook is not offering true 50/50 odds—the extra margin is their expected profit.
Understanding and calculating vig is crucial for:
- Comparing sportsbooks for the best price.
- Quantifying the true house edge.
- Finding (or confirming) arbitrage opportunities across venues.
ArbMonster measures live vig on 20+ US sportsbooks, updating every 15 minutes, and reports net opportunity sizes after all fees and margins.
Vig Calculator Formulas for Every Odds Format
American Odds
American odds are listed as positive (e.g., +150) or negative (e.g., -200). To find implied probability:
- For negative odds:
$\text{Implied Probability} = \frac{|\text{Odds}|}{|\text{Odds}| + 100}$ - For positive odds:
$\text{Implied Probability} = \frac{100}{\text{Odds} + 100}$
Decimal Odds
Decimal odds (e.g., 1.91) are common outside the US. The formula:
$\text{Implied Probability} = \frac{1}{\text{Decimal Odds}}$
Fractional Odds
Fractional odds (e.g., 5/2) are used in some markets, especially the UK:
$\text{Implied Probability} = \frac{Denominator}{Numerator + Denominator}$
Calculating Vig/Overround
Once you have all implied probabilities:
- Add them together.
- Subtract 1 (or 100% if using %).
$\text{Vig} = (\text{Sum of Implied Probabilities}) - 1$
Express as a percentage for the hold.
Worked Example: Calculating Vig for an NFL Spread
Suppose the odds are as follows:
| Team | American Odds | Decimal Odds |
|---|---|---|
| Dallas Cowboys | -110 | 1.91 |
| New York Giants | -110 | 1.91 |
Step 1: Convert Odds to Implied Probability
For -110:
$\frac{110}{110 + 100} = \frac{110}{210} \approx 0.5238$
So each side is 52.38% implied probability.
Step 2: Add Implied Probabilities
$0.5238 + 0.5238 = 1.0476$
Step 3: Subtract 1 to Find the Vig
$1.0476 - 1 = 0.0476$ (or 4.76%)
Result: The sportsbook hold is 4.76%. This is the classic "-110/-110" vig.
Other Example: Three-Way Moneyline (Soccer)
| Outcome | Odds | Decimal |
|---|---|---|
| Home | +120 | 2.20 |
| Draw | +240 | 3.40 |
| Away | +210 | 3.10 |
Calculating implied probabilities:
- Home (+120): $\frac{100}{120 + 100} = 0.4545$
- Draw (+240): $\frac{100}{240 + 100} = 0.2941$
- Away (+210): $\frac{100}{210 + 100} = 0.3226$
Sum: $0.4545 + 0.2941 + 0.3226 = 1.0712$
Vig: $1.0712 - 1 = 0.0712$, or 7.12%
Using an Online Vig Calculator
Manual math can get tedious, especially for multi-way markets. ArbMonster's vig calculator lets you paste or type odds in any format—American, decimal, fractional—and instantly outputs the implied probabilities and total vig, for two-way or multi-way markets.
For more methods, see the ArbMonster glossary entry on vig.
Why Vig Varies: Real-World Observations
- Most US sportsbooks keep vig between 4% and 6% for spreads/totals, but can run 8%+ on moneylines or props. See live vig rankings.
- European books sometimes offer lower hold, especially on soccer.
- Prediction markets like Kalshi and Polymarket charge explicit taker fees instead of hidden overround; see venue fee schedules.
Key Takeaways
- Vig is the sportsbook's built-in margin, measurable from odds using simple formulas.
- You can calculate vig for any odds format by converting to implied probabilities and summing.
- A vig calculator automates this process and works for 2-way or multi-way markets.
- Vig varies by market type and book; lower vig means better value for bettors and traders.
- ArbMonster measures live sportsbook and prediction market margins, net of all fees, for real-world arbitrage scanning.
FAQ
Q: What is the difference between vig, overround, and hold?
Vig, overround, and hold all refer to the sportsbook's built-in margin. "Vig" is most common in the US; "overround" is the sum of implied probabilities above 100%; "hold" is the percentage of stakes the book expects to keep. All are calculated the same way.
Q: How do I calculate vig for a parlay or multi-leg bet?
To find the vig for a parlay, first calculate the implied probability and vig for each leg, then multiply the decimal odds to get parlay payout, and compare to the true probability of all legs hitting. Parlay vig is usually higher due to compounded margins.
Q: Does a higher vig always mean worse odds for bettors?
Generally, yes. A higher vig means the book is taking a larger cut, so the odds are less favorable. Lower vig means more of the true probability is paid out to bettors. But always compare across books and markets for the best value.
Q: Where can I find a good online vig calculator?
The ArbMonster vig calculator handles all odds formats, both two-way and multi-way markets, and updates real sportsbook vig rankings every 15 minutes.
ArbMonster is a data service. Nothing here is financial or betting advice; markets carry risk, venues have age and jurisdiction restrictions, and you are responsible for verifying everything before acting.