Why use a fraction of Kelly
The full Kelly criterion computes the mathematically optimal stake to maximize long-run bankroll growth, but it requires a perfect probability estimate — something no bettor actually has. That's why most disciplined bankroll managers use a quarter or half Kelly: expected growth drops only slightly, while variance and the risk of a losing streak drop far more.
This calculator doesn't promise profit. It only translates your estimate into a consistent bet size, so that a run of misjudged bets doesn't erode your entire bankroll. Bankroll management is what separates bettors who work from a method from those working on impulse.