The standard way to strip vig from sportsbook odds is proportional devigging. It works on most markets. It doesn't work on all of them. This lesson is the longer story: three devigging methods, when each is right, and the one you should default to.
The setup
Every devigging method does the same job: takes the implied probabilities from a vigged market and converts them into a fair-probability estimate that sums to 100%. They differ in how they remove the vig.
The three you'll see in practice:
- Equal-multiplier (proportional) — the simplest, the standard
- Additive (logit / log-odds shift) — a small refinement
- Power method (Shin or similar) — used for asymmetric markets
For most main markets, all three give answers within a few tenths of a percent. The differences matter at the extremes — heavy favorites, longshots, and three-way markets.
Method 1 — Equal-multiplier
The default. Take the implied probabilities, normalize them so they sum to 1.
Example: Lakers -180 (64.3% implied), Celtics +160 (38.5% implied), sum 102.8%.
- Lakers no-vig = 64.3 / 102.8 = 62.5%
- Celtics no-vig = 38.5 / 102.8 = 37.5%
Assumption: the book applies vig evenly across both sides. Real for most markets. Slightly wrong at extremes.
Use it for: spreads, totals, moneylines at reasonable odds, props on main markets.
Method 2 — Additive (logit shift)
Slightly more accurate at the extremes. Instead of scaling probabilities multiplicatively, it shifts them in log-odds space.
The intuition: at -1000 odds (90.9% implied), shaving 1% off costs much less in payout terms than shaving 1% off a 50/50 line. A multiplicative shave under-corrects the favorite.
The math is messier — typically computed in code rather than by hand. The result: heavy favorites devig a little lower (more favorable for fading them), heavy underdogs devig a little higher (less generous payouts implied).
Assumption: vig is uniform in log-odds, not in probability.
Use it for: lines where one side is heavily favored — moneylines on big-favorite games, alt-line markets, futures with one dominant outcome.
Method 3 — Power method (Shin)
The most sophisticated of the three. Designed for markets where the vig is asymmetric — for example, when the book is structurally biased against the underdog because of "informed bettor" risk.
The Shin method introduces a parameter (typically called z) that adjusts how much extra correction is needed for the longshot side. For three-way markets (soccer 1X2, fight outcomes with draw), Shin tends to produce noticeably more accurate fair-probability estimates than the simpler methods.
The math is genuinely involved — solver-based, not closed-form. You don't compute this by hand. Sharp's odds-comparison tool gives you all three devigging options side-by-side.
Assumption: the longshot side carries a structural premium that needs separate correction.
Use it for: three-way markets (soccer, hockey regulation result, MMA with draw), longshot props, futures.
Which one to default to
For 90% of day-to-day betting, the equal-multiplier method is fine. Lower friction, fast enough to compute mentally, accurate enough to find real edge.
Switch to additive when you're working a heavy-favorite line or a moneyline at -300 or below.
Use the power method for three-way markets and longshots where the proportional method visibly under-devigs the favorite. Or just always use it for those — there's no cost to being more accurate beyond a click in the tool.
When devigging breaks entirely
A few honest limits.
- Stale markets — if the line hasn't moved in hours on a market that should be reacting to news, no devigging method will produce a useful fair price. The market is wrong, period.
- Single-book devigging — devigging Pinnacle is a strong fair-price estimate. Devigging the only book that posts the line just removes their margin but doesn't tell you what fair is — that book might be 5% off true.
- Promotional lines — boosted prices, free-bet conversions, and welcome-offer odds aren't honest market prices. Don't devig them — back them out separately.
The bottom line
Default to proportional. Know that the additive and power methods exist for the edge cases. Use Sharp's odds-comparison tool to compute all three at a glance so the method choice never slows you down. The goal is a fair-price estimate you trust — once you have it, the EV math is the same regardless of which method got you there.