No-Vig Fair Odds Calculator

How to use it

1. Enter both prices of one market from the same book, in any format.
2. For a soccer match result or any other three-way market, add the draw.
3. Pick a method; proportional is the usual default.
4. Optionally enter a price from another book to see its expected value against the fair odds.

The formula

Turn every price into its implied probability, measure how far they overshoot 100%, and scale them back.

implied = 1 / decimal, for each outcome
vig (overround) = sum of implied - 1
hold = 1 - 1 / sum of implied
fair probability (proportional) = implied / sum of implied
fair decimal = 1 / fair probability

-150 / +130: the prices imply 60.0% and 43.5%, 103.5% together. The vig is 3.5% and the hold 3.4%. Proportionally, the fair chances are 58.0% (-138) and 42.0% (+138). The power method gives 58.4% and 41.6%, the additive 58.3% and 41.7%.

• Proportional. Divides each side's implied probability by the total. The usual default.
• Power. Raises every implied probability to one power so they sum to 1, which takes more of the margin from the longer price.
• Additive. Takes the same share of the margin off every side.

Edge cases

• Use one book's prices for both sides. Prices from two books can add up to under 100%, which is not a margin to remove; the calculator flags it.
• The methods agree on an even market: -110 / -110 is 50.0% each by all three. They differ most on long prices.
• Three-way markets usually carry more margin than two-way ones, and the draw soaks up part of it; the table below shows the closing hold of each.
• A market with only one price listed cannot be devigged: the other side is what tells you the margin.