Find the bet or position size that maximizes long-run compound growth. Size a wager from win probability and payoff, or estimate continuous-Kelly leverage from a ticker's return history — then dial it back with fractional Kelly to tame the drawdowns.
The Kelly criterion picks the fraction of capital that maximizes expected logarithmic (compound) growth. It is optimal only asymptotically and assumes you know the true odds — real edges are uncertain and estimated with error, so full Kelly risks severe drawdowns and long underwater stretches. Fractional Kelly (half or quarter) gives up a little growth for much lower volatility and is what most practitioners actually use. The ticker mode's continuous Kelly assumes daily returns are i.i.d. normal and stationary, ignores fat tails, autocorrelation, transaction costs and financing, and is extremely aggressive on a single asset. Educational only - not investment advice.