Do you have a mechanical framework to help you decide how much cash (dry powder) to keep in your portfolio?

My current framework is to keep roughly 10%–20% of my portfolio in cash during bull markets. As my stock positions appreciate, my cash percentage naturally falls. When it gets too low, I trim some positions and rebuild the cash reserve.

The idea is:

Have dry powder available for market dips.

Prevents a few positions from becoming too large.

It sort of forces me to see dips as buying opportunities instead of causing me to sell because of fear.