W Atlas of odds WikiOne
Guide / market mechanics

What is bookmaker margin?

Bookmaker margin, often called overround, is the built-in cushion that turns a fair market into a profitable one for the operator. It is one of the cleanest concepts for showing why the same event can be priced differently across sites.

Pairs with expected value Useful for sportsbook education Supports natural comparison links
Meaning Example Use in practice

What margin means in plain language

In a perfectly fair two-way market, the implied probabilities would add up to exactly 100%. A bookmaker usually prices the same market so that the total is higher than 100%. That extra percentage is the margin.

A two-way market example

If both sides of a market are priced at 1.91, each side implies a probability of 52.36%. Add them together and the market totals 104.72%.

Selection Odds Implied probability
Side A 1.91 52.36%
Side B 1.91 52.36%
Market total - 104.72%

In this case, the overround is 4.72%. The market is not fair. The bookmaker has priced in a margin.

Margin = total implied probability - 100%

Why readers should care

Margin explains why one sportsbook can feel more "expensive" than another. It also shows why expected value is easier to find in sharper markets or after comparing multiple price sources. That is where pages on OddsRex or Finnish bookmaker comparisons on Kerroinkuningas become a logical next click instead of a forced promotion.

Margin is one of the best examples of why educational content and comparison content can complement each other cleanly. The explainer teaches the mechanic. The comparison page helps a reader act on it.