Bookmaker margin & fair-odds calculator
See the margin baked into a market and the true, no-vig prices.
Every bookmaker builds a margin into their prices, so the implied probabilities of a market add up to more than 100%. Enter the odds for each outcome to see that margin, and the fair (no-vig) odds you'd get if it were stripped out — a quick way to judge whether a price is sharp and to compare books.
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What it does
- Bookmaker margin (overround) for the whole market
- No-vig fair odds and probability for each outcome
- Implied vs fair probability, side by side
- Spots an underround (negative margin) where the market is in your favour
How to use it
- 1Enter every outcome's odds. Add the decimal odds for each outcome in the market.
- 2Read the margin. See the total implied probability and the bookmaker's margin.
- 3Compare fair odds. The table shows the no-vig fair odds and probability per outcome.
What powers this
This calculator runs entirely in your browser. There's no account, no API key and no feed — nothing you type leaves the page. The maths is the same commodity matched-betting and value arithmetic used across the industry, implemented carefully and unit-tested.
Embed it on your site
Paste this where you want the margin & fair-odds calculator to appear. The script auto-mounts every widget on the page; swap data-or-theme for light, dark or transparent.
<div data-or-widget="margin" data-or-theme="light"></div>
<script src="https://oddsrelay.io/widgets/oddsrelay-widgets.js" async></script>Questions
- What is a bookmaker's margin?
- The margin (or overround / vig) is the edge a bookmaker builds into their prices. Add up the implied probabilities of every outcome — the amount over 100% is the margin.
- What are no-vig fair odds?
- Fair odds are the prices with the margin removed proportionally, so the probabilities sum to exactly 100%. They're the market's best estimate of the true chances, useful for spotting value.
- Can the margin be negative?
- Yes — if the implied probabilities add up to under 100% it's an underround, and backing every outcome would guarantee a profit. That's the arbitrage case, and it's rare.
18+ · Data product for licensed operators. Please gamble responsibly.
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