Margin is the built-in profit a bookmaker adds to betting odds, also known as the bookmaker’s overround.

It represents the difference between true probability and the odds offered.

How it works

• Bookmakers adjust odds so total implied probability exceeds 100%

• The excess percentage is the bookmaker’s margin

• Lower margin = better value for bettors

Example

• Two-outcome event

• Odds imply probabilities totaling 105%

• Margin = 5%

Key characteristics

• Present in all betting markets

• Higher on niche or low-liquidity markets

• Accumulates strongly in accumulators and bet builders

Important note
Even accurate predictions can lose money long term if bets are placed in high-margin markets.