Bankroll and units
Your bankroll is money set aside only for betting, money you can afford to lose. A unit is your normal bet, usually 1 to 2% of it. With $500, a unit is $5 to $10.
Kelly sizing
The Kelly formula sizes each bet by its edge: a bigger edge gets a bigger stake. Full Kelly grows fastest on paper but swings hard, and it assumes your win chance is exact. It never is.
Why we use a quarter Kelly
A quarter of the Kelly stake keeps most of the growth with far smaller swings, and it forgives small errors in the fair price. Our suggested stakes use it. Set your bankroll in your account and the board sizes each pick for you.