Margin calculator
Every betting market charges a fee, and it's printed nowhere. Type the odds of each outcome and read what the book is really keeping — and what the fair prices would have been without it.
leave empty for a two-way market
- Book total
- 104.8%
- Margin
- 4.8%
| Outcome | Odds | Implied | Fair prob. | Fair odds |
|---|---|---|---|---|
| Home | 2.10 | 47.6% | 45.4% | 2.20 |
| Draw | 3.40 | 29.4% | 28.1% | 3.56 |
| Away | 3.60 | 27.8% | 26.5% | 3.77 |
These three prices sum to an implied 104.8% — the 4.8% above 100% is the operator's cut, and each price overstates its outcome's real chance by roughly that share.
What the margin is
Convert each price to an implied probability (one divided by the decimal odds) and sum the market. A fair book would total exactly 100%; the excess is the overround — the operator's structural edge, collected whichever outcome lands. The conversion arithmetic, with worked examples in every odds format, is in how to convert odds to implied probability, and you can go price-by-price with the odds converter.
How the fair numbers are computed — and their limit
This tool removes the vig proportionally: each implied probability is divided by the book total, so the outcomes keep their relative sizes and sum to 100%. That is the standard first-pass method and it is honest to say it isn't perfect — bookmakers don't spread their margin evenly, loading more of it onto long shots than onto favourites, so a proportional de-vig slightly flatters outsiders. For judging whether a price beats a probability estimate, it is more than good enough; for measuring a record properly, closing prices are the yardstick, as argued in value bets and closing odds.
Why this number matters more than any tip
The margin is the hurdle every bet must clear before skill counts for anything: at a 5% overround you need to be right 5% more often than the market thinks just to break even. It compounds brutally in accumulators — the accumulator calculator shows that arithmetic — and it varies between books and markets, which makes comparing it one of the few genuinely free improvements available to any bettor. Our own match pages show the market's de-vigged probabilities next to the model's raw ones, so the comparison is always margin-free.