Vince’s Optimal F for Compounding Trade Returns and Position Sizing
Summary
The article presents Ralph Vince’s optimal-f approach to money management. It explains how compounding makes the path of account equity depend on the fraction of capital risked, and why maximizing the stake does not necessarily maximize long-run growth. For a known win probability and payoff ratio, it introduces the Kelly formula; for an observed series of trade results, it describes searching numerically for the fraction that maximizes the product of holding-period returns. It also shows a way to plot growth across candidate fractions.
Examples compare different stake fractions and sequences of wins and losses, then illustrate how combining strategies with different correlations can change outcomes. The article describes converting fixed-lot tester results into a trade-profit series for estimating f and building position-sizing modules in MQL5. Its examples are simplified, and the maximizing fraction can imply very large drawdowns. The estimate depends on the input trade history and assumes it is useful for future trading; position sizing cannot turn a losing system into a profitable one.
Key ideas
- Compounding causes losses and gains to affect future capital, so stake size changes long-run outcomes.
- Optimal f seeks the stake fraction that maximizes the product of holding-period returns across a trade sequence.
- Kelly’s formula applies to simplified cases with stable win probability and payoff ratio.
- The article uses numerical search on historical trade results to estimate f for empirical systems.
- A growth-maximizing fraction can expose an account to severe drawdowns, and diversification effects depend on correlation.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.