Devigging Methods: Three Ways to Strip the Juice

Removing the vig sounds like one calculation, but there are several — and they don't all give the same answer. The method you pick changes your fair probability, and on thin edges that can flip a bet from good to bad.

Why the method matters

Every posted line is padded with the vig — the book's margin, which makes both sides' implied probabilities add up to more than 100%. That excess is called the overround. Devigging means redistributing the real probability across the outcomes so it sums back to a clean 100%.

The catch: there's no single "correct" way to decide how much of that overround belongs to each side. Should the vig be split proportionally? Split evenly? Weighted toward the favorite or the longshot? Each answer is a different devigging method, and each produces a slightly different fair number from the exact same line.

The three methods

Let's run all three on the same market: a favorite at −130 and an underdog at +110. First, the raw implied probabilities:

1 — Multiplicative (proportional)

The standard. Divide each side's implied probability by the total. Each outcome keeps its proportional share of the market, so a bigger favorite absorbs a bigger slice of the vig removal:

Simple, fast, and the industry default. It assumes the vig is spread proportionally to each side's probability.

2 — Additive (equal split)

Subtract the vig equally from each side. With 4.14% of overround across two outcomes, each side gives back half — 2.07%:

This treats the vig as a flat toll charged the same to every outcome regardless of how likely it is. It's easy to reason about but tends to over-tax longshots.

3 — Power / Shin (bias-corrected)

The most sophisticated. Instead of dividing or subtracting, it raises each implied probability to an exponent k chosen so the results sum to exactly 1. That exponent corrects for the favorite-longshot bias — the well-documented tendency of books to shade longshots too generously and favorites too tightly:

The Shin model is a close cousin that adds an "insider trading" parameter, but the intuition is the same: pull probability away from longshots and toward favorites, rather than treating both sides identically. On lopsided lines this correction can be substantial.

Side-by-side comparison

Here's what the same −130 / +110 market looks like under all three methods:

Method	Fair P (Fav)	Fair P (Dog)	Fair dog odds
Multiplicative	54.27%	45.73%	+119
Additive	54.45%	45.55%	+120
Power (k≈1.0625)	54.54%	45.46%	+120

Which method pros prefer

There's no universal winner, but the working consensus among sharp bettors:

• Multiplicative is the sane default — accurate enough on balanced two-way markets, trivial to compute, and rarely far off.
• Additive is the weakest of the three for real money. Splitting the vig equally systematically overcharges longshots, so it's mostly a teaching tool.
• Power / Shin is the choice for lopsided lines and longshot markets, where favorite-longshot bias is strongest. It better matches how prices actually behave, at the cost of more computation.

The most disciplined approach isn't picking one method and trusting it forever — it's comparing methods. When all three agree that a bet is +EV, you can be confident. When they disagree, the edge is thin enough that you should treat it with suspicion. That disagreement is itself a signal.

Doing it right, on every line

Running one market through one method takes a minute. Running thousands of markets through the right method, live, as lines move — that's the real work. Iron Marker devigs sharp reference lines automatically, applies the appropriate method for each market's shape, and compares the fair number against every US book so you only see genuinely +EV bets.

Frequently asked questions

What are the different ways to remove the vig from a betting line?

The three common devigging methods are multiplicative, additive, and power (with Shin as a related, more academic variant). Multiplicative divides each side's implied probability by the market total — the overround — scaling every outcome down proportionally. Additive instead subtracts an equal share of the vig from each side. Power raises each implied probability to a fitted exponent chosen so the results sum to 100%, which removes proportionally more vig from longshots — closer to how books actually construct their prices. All three start from the same posted odds and end with probabilities summing to exactly 100%, but they distribute the vig differently between the sides, so each produces slightly different fair probabilities from the same line.

Does the devigging method actually matter?

Yes — and precisely in the spots where you can least afford to be sloppy. On a balanced two-way market like −110 / −110, every method lands within a rounding error of the others, so the choice is academic. But as a market gets lopsided — a heavy favorite against a big underdog, a longshot prop — the methods diverge meaningfully, because each makes a different assumption about where the book hides its margin. Since most real +EV opportunities are thin edges of a few percent, a gap of even half a point of probability between methods can flip a marginal bet from playable to pass. The rule of thumb: the more lopsided the market, the more the method matters.

Which devigging method do professional bettors use?

Multiplicative is the default — simple, transparent, and accurate on the balanced markets where most betting volume lives, which is why most tools use it as the baseline. But betting markets systematically over-price longshots relative to favorites (the favorite-longshot bias), and multiplicative devigging ignores that, crediting longshots with more probability than they deserve. So many pros switch to power or Shin methods on lopsided lines, since those push more of the vig onto the longshot side, matching the observed bias. The most common professional habit isn't loyalty to one formula at all: it's running multiple methods on marginal bets and only firing when the edge survives the most conservative one — filtering out edges that are artifacts of the math.

What is the favorite-longshot bias and why does it matter for devigging?

The favorite-longshot bias is the well-documented tendency of betting markets to over-price longshots and slightly shade favorites, relative to true probabilities — bettors overpay for lottery-ticket payouts, and books load a disproportionate share of their margin onto the longshot side. This matters for devigging because the multiplicative method removes vig proportionally from every outcome. If the vig actually sits mostly on the longshot, a multiplicative devig leaves the longshot's fair probability too high — which can make bad underdog bets look +EV when they aren't. Power and Shin methods exist precisely to correct for this by stripping more margin from the longshot side. If your +EV finds skew heavily toward big underdogs, your devig method is the first suspect.

Which devigging method should I use for player props?

Treat props with more suspicion than main lines, whatever formula you run. Prop markets carry heavier vig than sides and totals, are frequently lopsided, and get priced with less care — three conditions that magnify the differences between devigging methods. A sensible workflow: use multiplicative as the baseline when both sides are posted and reasonably balanced, but re-check marginal edges with a power devig before betting, especially plus-money longshot sides where favorite-longshot bias runs hottest. And make sure you're devigging a genuine two-sided market: if a book posts only the over, you can't extract a fair number from that book alone — you need a sharp book's two-sided price on the same prop as your reference.

Iron Marker is an analytics tool, not a sportsbook, and this guide is educational — not betting or financial advice. Odds shown are illustrative. Must be 21+. Problem gambling? Call 1-800-GAMBLER.