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No-vig fair odds, explained
Arbs research desk · Updated 2026-11-01 · Reviewed 2026-11-01 · 2 min read
The short answer: No-vig odds are a book’s line with its margin removed. Convert each side to an implied probability, divide each by their total so they add to 100%, and convert back. A −110/−110 line becomes +100/+100.
Why the probabilities add to more than 100%
A book shades every side so its implied probabilities add to more than 100%. That excess, the overround, is how the book earns regardless of who wins.
implied probability q = 1 ÷ d for each side; overround O = sum of q − 1
At −110/−110 each side implies 52.38%, the total is 104.76%, and the overround is 4.76%.
The multiplicative method
Divide each implied probability by the total. It takes margin off every side in proportion to its size.
p = q ÷ (sum of all q)
Worked example: Devigging −150 / +130
- Implied: −150 is 150 ÷ 250 = 60.0%; +130 is 100 ÷ 230 = 43.5%
- Total: 103.5%, so the overround is 3.5%
- Fair: 60.0 ÷ 103.5 = 58.0% and 43.5 ÷ 103.5 = 42.0%
The fair line is about −138 / +138.
The power method
Books usually put more margin on the longshot, the favourite–longshot bias. The power method finds the exponent k that makes the implied probabilities, raised to k, add to exactly 1. Because a small number shrinks faster under a power above 1, it takes more off the longshot.
find k so that the sum of qᵏ is 1; then p = qᵏ
On the −150 / +130 line, k is about 1.053, giving 58.4% and 41.6%, or −140 / +140.
| Method | Favourite | Underdog | How the margin is removed |
|---|---|---|---|
| Multiplicative | 58.0% | 42.0% | In proportion to each side |
| Additive | 58.3% | 41.7% | An equal amount from each side |
| Power | 58.4% | 41.6% | More from the longshot |
Three-way markets
Soccer lines carry a draw, and the same idea extends to any number of outcomes.
Worked example: Home +150, draw +230, away +190
- Implied: 40.0%, 30.3% and 34.5%, a total of 104.8%
- Multiplicative fair: 38.2%, 28.9% and 32.9%
- Fair odds: +162, +246 and +204
The overround is 4.8%, spread across all three outcomes.
Shin’s method goes further for three-way markets: it models the margin as the book protecting itself against better-informed bettors. Inside its model Arbs uses the power method on two-way lines and Shin’s on three-way soccer lines.
Using fair odds
Once you have a fair probability, any price that pays more than it is +EV. A sharp book’s fair line compared with Polymarket, or with a softer book, is the simplest way to find value.
Worked example: Fair 58.0% against a 55¢ Polymarket ask
- Fee at 0.05: 0.05 × 0.55 × 0.45 = 1.24¢, so the cost is 56.24¢
- EV = 0.580 ÷ 0.5624 − 1
+3.1% per dollar staked, by the book’s fair line.
Try it in the no-vig calculator, then the EV calculator.
Try it: No-vig calculator
Frequently asked questions
What does no-vig mean?
The odds with the bookmaker’s margin removed, so the implied probabilities add to exactly 100%.
Which devig method is best?
For two-way lines near even money the methods agree to within a point. On big favourites and three-way soccer lines the power and Shin methods usually fit results better than the multiplicative one.
Which book should I devig?
The sharpest one available for that market, usually a high-limit book or a consensus of several. A soft book’s fair line is still shaded by its customers.
Is the no-vig line the true probability?
It is the book’s estimate without its margin. Sharp lines are good estimates, but they still move with news.