Estimating Strategy Capacity from Liquidity and Market Impact

Summary

The document explains why a strategy’s maximum capital capacity cannot be calculated from backtest returns and volatility alone. Capacity depends on the strategy’s logic and trading frequency, the liquidity and order book depth of its instruments, the size of positions held, and investors’ tolerance for risk. Entry and exit duration also matter: longer execution windows in higher-volume markets can reduce market impact, while high-frequency strategies may need to assess liquidity at individual moments.

Key ideas

• Strategy capacity is driven mainly by liquidity, execution costs, and the design of the strategy rather than backtest return and volatility statistics alone.
• Estimate how trading costs change as capital increases, using historical market or order-book data where possible.
• Include slippage and fill probability in backtests, while recognizing that impact may rise nonlinearly with order size.
• Diversifying across more stocks can reduce per-stock impact, but excessive diversification may weaken returns.
• Use out-of-sample or live results and gradually scale positions to check whether actual execution matches estimates.

Tags

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.