No-vig probability calculator
Compare a complementary YES/NO pair by normalizing its two prices to a total of 100%. This is a proportional estimate, not a way to discover the true probability or a platform's fee schedule.
No-vig fair odds
Normalize two complementary outcome prices to a total of 100¢. This proportional estimate is not the true probability, and an order-book spread is not a platform fee.
The two quoted prices exceed 100¢ by 3.0¢. This is not a fee estimate.
How to use this calculator
- Choose two outcomes that are mutually exclusive and cover all possible settlements in the model.
- Enter comparable quoted prices for both sides, using asks if comparing the cost of buying both.
- Read the normalized probabilities and check the spread, available size and fees separately.
Formula
- Total = YES price + NO price
- Normalized YES = 100 × YES price / Total
- Normalized NO = 100 × NO price / Total
- Overround in cents = Total − 100
Worked example
YES at 55¢ and NO at 48¢ add to 103¢. Proportional normalization gives 53.40% for YES and 46.60% for NO. The 3¢ excess describes this pair of quotes; it is not automatically a commission charged by an exchange.
Assumptions and limitations
This method distributes the excess proportionally. Other normalization methods can produce different estimates. Exchange order-book spreads and bookmaker overround are not identical concepts. A pair below 100¢ is not sufficient evidence of executable arbitrage.
Common questions
Are normalized probabilities the true odds?
No. They are the result of a chosen normalization method applied to your inputs. They do not validate either quote or estimate an outcome independently.
Can I enter YES bids and NO bids from an order book?
Not to estimate the cost of buying both. Bids describe what someone will pay you; use the corresponding asks for a purchase comparison.
Examples are our arithmetic illustrations. Linked references explain the underlying market mechanics or model; they do not endorse a result or a trade.