How much to bet

A bankroll is money set aside for betting that you could lose entirely without it changing your life. Pick the number first. A unit is 1% of it — so a $1,000 bankroll is $10 a unit, and every stake in the app is quoted against that.

Kelly, and why a fraction of it

The Kelly criterion sizes each bet by its edge — bigger edge, bigger stake — and maximises long-run growth. Its catch is that it is only optimal if your win probability is exactly right, and yours is a de-vigged consensus: very good, not exact.

Over-betting punishes you far harder than under-betting. The growth curve falls off a cliff past the optimum and merely flattens below it, so everyone serious runs a fraction of full Kelly.

Quarter Kelly is what most profitable bettors actually run, and it is what this app suggests out of the box. It matters most on the markets where books are least confident: a main line at -110/-110 is tightly priced, but whether a player gets three rebounds or four is genuinely hard, the vig is fatter, and your estimate of the fair price is shakier. Sizing down absorbs that.

Sanity-check the number

If a suggested stake looks enormous, something upstream is probably wrong — a stale price, a book that has already moved, a market with too few quotes behind it. The app caps any single suggestion at 5% of a bankroll for exactly this reason, but the instinct is worth keeping.