Betting Units and Bankroll Management
A unit is a fixed share of your bankroll, and sizing bets in units instead of dollars is the discipline that keeps variance from wiping you out. Here is how units, fractional Kelly, and bankroll caps fit together.
A unit is a fixed fraction of your bankroll, usually 1%. Sizing bets in units instead of dollars is the most important discipline in betting, because it ties your stake to your bankroll and your conviction rather than to how you feel on a given night.
Why units, not dollars
Talking in units keeps strategy separate from the size of your wallet. A 2-unit play is a 2-unit play whether your bankroll is $500 or $50,000. It also makes results comparable over time, and it stops a hot or cold streak from quietly changing your bet size.
Fractional Kelly
The Kelly criterion is a formula for the mathematically optimal stake given your edge and the odds. Full Kelly is too aggressive for real betting, where your edge is an estimate rather than a known quantity, so Fairline uses a fraction of Kelly and caps the result. Bigger edges earn bigger stakes, within limits.
Stakes scale with edge, from roughly 0.5u on a marginal play up to a capped maximum on the strongest. A per-night exposure cap stops the model from loading the whole bankroll onto a single slate.
The one thing you control
You cannot control variance, the schedule, or whether a star sits out. You can control how much you risk. Flat, unit-based sizing with a sensible cap is the difference between surviving a normal losing stretch (see variance) and busting out during one.