Line gaps where both bets win; ranked by expected value, not window width
A middle is two bets on opposite sides of a line, at different numbers, placed so that a result between the two numbers wins both bets. It usually appears when one book moves its line and another has not caught up.
Most middles miss, and a miss costs a small amount — roughly the two books' margin. The board ranks middles by expected value, weighing how often the gap is likely to land against what a miss costs, not just by how wide the window is.
Book A has a total at Over 44.5 at -110. Book B has the same game at Under 47.5 at -110.
Bet $110 on each. A final total of 45, 46 or 47 wins both bets: +$200.
Any other total wins one bet and loses the other: -$10.
The break-even hit rate is 10 ÷ 210 = 4.76%. The board estimates how often the result lands in the window and ranks by the expected value that implies.
Step by step: How to middle a bet, step by step.
arbitrage calculator — size both sides of a middle for any two prices, free.
how to middle a bet — the step-by-step version, with a worked example.
Two bets on opposite sides of a spread or total at different numbers, so that a result between the numbers wins both. When it misses, one bet wins and one loses, for a small net loss.
Only when the chance of hitting the window outweighs the cost of missing. A three-point window around a common final score is worth far more than the same width somewhere results rarely land.