Rule

Ignore the '50% of max credit, or 21 DTE' management convention.

What it means

It was popularised by a broker with a direct commercial interest in trade frequency, and the best independent test found the PASSIVE version beat the managed one on both CAGR (5.46% vs 4.44%) and Sharpe (0.67 vs 0.52) - before slippage, which biases toward the active version. And a 21-DTE stop is undefined when you enter at 7 DTE.

What to do instead

Close when the expected remaining P&L from simulation falls below the expected round-trip exit cost plus a charge for remaining tail exposure. A computed decision, not a convention.