Glossary
Key number
A key number is a final margin that games land on far more often than others, because scoring comes in fixed chunks. In many sports, spreads and totals cluster around these figures, so moving a line across one changes how often a bet wins by a meaningful amount.
Not every final margin is equally likely. When points are scored in set amounts, some margins repeat over and over while others barely appear. Those repeat offenders are the key numbers, and they matter far more than the ones in between.
Imagine a league where scores tend to build in threes and sevens. Over a long history, margins of 3 and 7 show up again and again, while a margin of 5 or 8 is comparatively rare. A point spread set right on top of one of those common margins is doing very different work than one set half a point away from it.
Why the gap between numbers is uneven
The difference between a spread of 2.5 and 3.5 is not the same as the difference between 4.5 and 5.5, even though both look like a single point. The first pair straddles a common margin, so a huge share of games settle inside that one-point gap. That is why buying points across a key number costs more, and why line movement past one is a bigger deal than the raw number suggests.
They shift by sport
Key numbers are specific to how a given sport scores. The margins that dominate one sport may be meaningless in another, so learn the pattern for the games you actually follow rather than assuming a universal set.
The same logic applies to an over-under, where certain totals land on the scoreboard more often than their neighbors.