Bookmaker margin calculator and fair odds
Enter the prices of every outcome in one market. The calculator shows the margin built into them and the prices you would get without it.
Each outcome with the margin removed
| Outcome | Price offered | Implied chance | Chance without margin | Fair price |
|---|---|---|---|---|
| Outcome 1 | 1.91 | 52.36% | 50.00% | 2.00 |
| Outcome 2 | 1.91 | 52.36% | 50.00% | 2.00 |
How the margin is found in a set of prices
Turn every price into an implied chance by dividing one by it, then add the chances up. In a market with no margin they would total exactly 100%. Whatever stands above that is the margin, also called the overround, the vig or the juice. Prices with it taken out are known as no-vig odds. Dividing each implied chance by the total gives chances that add up to 100% again, and one divided by such a chance is the fair price.
Worked example
Both sides of a market stand at 1.91. Each implies 52.36%, so the book is 104.71% and the margin is 4.71%. Without it both sides would be priced 2.00. The market pays back 95.50% on average, a cost of 4.50 for every 100 staked.
A price in another format can be turned into decimal first with the odds converter. When the best prices of several bookmakers push the book under 100%, the arbitrage stake calculator splits the money. The same idea in casino games is the house edge, priced out in the expected loss calculator.
What the margin figure leaves out
- It needs every outcome of the market. Leave one out and the margin comes out too low.
- Removing the margin in proportion is one method among several. The true chances may sit elsewhere.
- A low margin makes a market cheaper to bet on. It does not make any single bet a good one.
Questions about bookmaker margin
What margin do two prices of 1.91 carry?
The book adds up to 104.71%, a margin of 4.71%. The fair price of each side is 2.00.
How is the margin read in a three-way market?
The same way, with three prices. Prices of 2.10, 3.40 and 3.60 carry a margin of 4.81%, and the fair price of the first outcome is 2.20, a chance of 45.43%.
Is margin the same as house edge?
It plays the same part. A casino game with a fixed RTP keeps a known share of every bet, and a bookmaker keeps the margin on average across the market.
Does a fair price mean the bet has value?
No. A fair price only removes the margin from the view of the bookmaker. A bet has value when your own estimate of the chance is higher than the one the price implies.