Paste in the two (or three) prices a book is offering. This strips out the bookmaker margin and gives you the fair win probability and fair odds for each side, plus the vig. Type any price and it recomputes instantly.
| Outcome | Your price | Implied | Fair prob | Fair decimal | Fair American |
|---|
Built on the same math ParlayAPI runs. This is the exact
devig used by ParlayAPI's /v1/devig and /v1/ev
endpoints, applied at scale across 30+ sources instead of one line at a time.
You can pull the live odds to feed this calculation straight from the API:
create a free key or read the docs.
A bookmaker's prices always add up to more than 100% implied probability. That extra slice is the vig (also called the margin or juice). Devigging removes it so you can see what the book actually thinks each outcome's chance is.
p = 1 / decimal odds.fair decimal = 1 / fair probability, and to American if you prefer.
This is the proportional method (each probability is scaled by
the same factor, 1 / overround, which is why it is also called the
multiplicative method). It is the standard, transparent default. Other approaches
exist for splitting the margin unevenly between favorite and longshot (additive,
Shin, power) and can be a better fit for heavy favorites, but they need extra
assumptions; proportional makes none.
A note on words: the vig shown above is overround - 1, the margin
relative to a fair 100% market. The book's hold, the share of total
handle it keeps with balanced action, is the slightly smaller
(overround - 1) / overround. At -110/-110 the vig is 4.76% and the
hold is 4.55%. The hold calculator computes
both side by side.
Removing the vig tells you the market's fair price, not the true probability of the event. A single book can be wrong or slow. For a sharper estimate, devig a sharp market (or a consensus of several books) rather than the same book you are betting into, and compare that fair price against the price you can actually get. That comparison is exactly what an expected-value check does.
The prices a market would show if the bookmaker took no margin. A real market's implied probabilities sum to more than 100%; dividing each by that sum removes the margin, and converting back to odds gives the fair, no-vig prices.
Each -110 side implies 52.38%. Together they sum to 104.76%, so dividing each by 1.0476 gives exactly 50% per side. Fair odds are 2.00 decimal, or +100 American, on both sides.
The proportional (multiplicative) method: every implied probability is divided by the overround. Additive, power, and Shin methods split the margin unevenly and can fit heavy favorites better, but they need extra assumptions; proportional makes none.
No. It is the market's opinion with the margin removed. A single book can be wrong or slow. Devigging a sharp market, or a consensus of several books, gives a better reference point than devigging the book you plan to bet into.