Devigging — Removing the Bookmaker Margin to Find the True Line
Bookmaker odds bake in margin. Devigging strips the margin off so the remaining probabilities sum to 100% — that's your "true line".
Updated · 7 min read
Key takeaways
- Bookmaker raw probabilities sum to more than 100% — the excess is the overround (margin).
- Proportional devig is the simplest method and works well on 2-way markets.
- Shin devig accounts for informed-bettor bias — better on lopsided multi-way markets like horse racing.
- Power devig is used on highly multi-runner markets (motorsports, golf majors).
- Pick the right method per market shape — wrong devig produces fake +EV signals.
What "vig" actually is
When a bookmaker prices Lakers vs Celtics at 1.91 / 1.91, the implied probabilities sum to 104.8%. That extra 4.8% is the bookmaker's gross margin — the "overround" or "vig". Across millions of balanced bets, this guarantees the book profit.
Your job as a +EV bettor is to figure out what the underlying probabilities would be if the bookmaker took zero margin. That's "devigging" or "removing the vig".
Proportional devig
The simplest method. Each outcome's true probability is its share of the overround:
p_implied(Lakers) = 1/1.91 = 0.5236 p_implied(Celtics) = 1/1.91 = 0.5236 sum = 1.0472 (4.72% overround) p_true(Lakers) = 0.5236 / 1.0472 = 0.5000 p_true(Celtics) = 0.5236 / 1.0472 = 0.5000
Shin devig
Hyun Song Shin's model assumes some portion of the market is "informed" (insider/early money) and corrects for the asymmetric bias this introduces. Shin devig produces sharper probabilities than proportional when one side has heavy steam.
On a 2-way market where proportional says 60/40, Shin will usually pull both probabilities slightly toward 50/50, recognising that the favourite is partly overpriced by informed money.
When to prefer Shin
- Heavy public-money markets (popular AFL favourites, NRL Origin)
- Lopsided pre-match lines where one side is shorter than ~1.50
- Markets where you suspect significant insider participation
Power devig
Used on many-runner markets (horse racing, golf majors, motorsports). Raises each implied probability to a power k chosen so the adjusted probabilities sum to 100%. Handles the long-tail-favourite distortion that proportional and Shin can't.
Which method does Krok Odds use?
Krok Odds picks the devig method per market type:
For market-specific devig choices and the sharp-source weighting we apply, read the methodology page.
- H2H and totals (2-way) — proportional devig.
- Heavily lopsided pre-match lines — Shin devig as a sanity check.
- Multi-runner outright markets — power devig.
- Player props with 2-way line/total structure — proportional.
How to avoid fake +EV signals
The most common +EV false positive is using a soft AU bookmaker's devigged line as the "sharp" baseline. Devigging a soft book just reveals what the soft book thinks the true line is — which is wrong, that's why it's soft.
Always devig the actual sharp markets (international sharp baseline, Betfair Exchange) and compare AU corporate prices against those.
FAQ
Is devigging just dividing by the overround?
For 2-way markets, proportional devig is essentially that. For 3+ way markets, especially lopsided ones, you should use Shin or power devig instead — they account for asymmetric biases that proportional ignores.
Why do different devig methods give different answers?
They make different assumptions about how the bookmaker margin is distributed. Proportional assumes uniformly; Shin assumes informed-money bias on the favourite; power adjusts for long-tail distortions. Pick the method that matches the market structure.
Can I just use the sharp posted prices directly?
No — sharp markets still carry a small margin (1.5–2.5%). Devigging them gives you the cleanest p_true available, which is what you compare AU corporate prices against.
What overround should I expect at AU books?
2026 AU corporate H2H overround is typically 4–7% on majors, 8–12% on player props. International sharp markets sit at 1.5–3%. Betfair Exchange ranges 1–2% post-commission depending on liquidity.