Tom has the key adjustment: size the reserve against the portfolio-funded portion of spending, not the whole budget. The other thing worth doing is deciding in advance how you will refill it. A common approach is to top the buffer back up in any year the portfolio finishes positive, and leave it alone in years it does not. That rule turns the buffer into a working mechanism rather than a static pile of cash. Educational only, of course — your own plan may warrant something different.
