Bookmaker margin and overround: compare the real price

The short answer

Add the implied probabilities for every outcome. The amount above 100% is the market overround — a price signal, not a guaranteed operator profit.

Calculate the overround step by step

Start by converting every mutually exclusive outcome into implied probability: divide 1 by the decimal odds and multiply by 100. Include every outcome in the same market. In a football match market, that normally means home, draw and away; in a two-way market, include both sides.

Add the probabilities. A perfectly margin-free set of prices would total 100%. Commercial prices commonly total more. If two outcomes are both offered at 1.91, each implies 52.36%, producing a total of 104.72%. The 4.72 percentage points above 100 are the overround.

What the number does and does not show

Overround is a compact way to describe the total price built into one quoted market. It is useful when comparing the same market across services or tracking whether a market becomes more competitive as an event approaches.

It is not the operator's guaranteed profit on an individual event. Bets may not be distributed evenly, prices can move and the effective margin can differ by outcome. Overround also says nothing about whether your own probability estimate is accurate.

Remove the margin for a cleaner comparison

To create a simple margin-free estimate, divide each outcome's implied probability by the total implied probability. In the balanced 1.91 versus 1.91 example, 52.36 divided by 104.72 gives 50% for each side.

This proportional method is convenient, but it assumes the margin is distributed proportionally. Real markets can shade one outcome more than another. Use normalized probabilities as a comparison tool, not as a forecast.

How to compare markets responsibly

Compare identical settlement rules, outcomes and timestamps. One service may include overtime while another settles at the end of regulation. A lower overround does not compensate for unsuitable rules, weak consumer protections or spending beyond a planned limit.

Record the final available price because quotes can change quickly. If you calculate a margin from an old screenshot and compare it with a live market, the result is not meaningful.

• Use prices captured at the same time.
• Include every outcome in one market.
• Check settlement and void rules.
• Keep price comparison separate from outcome prediction.

Practical checklist

• Convert each decimal price with (1 / odds) × 100.
• Add all outcomes and subtract 100 to find overround.
• Normalize probabilities only for comparison.
• Compare identical rules and use a fixed spending limit.