The hybrid
The Yale spending rule is 70% of last year’s inflation-indexed spend plus 30% of a target rate times current assets. Universities cannot change the operating budget 20% after one endowment year; the blend is how they stop that. Typical teaching weights are 70/30. Spending follows markets, slowly. This is not a scholarship or fundraising calculator.
A household is not a university. There is no board, no tuition, no 50-year mission. What you are buying is smoothness. What you are selling is the ability to spend a windfall now, and the ability to cut hard after a crash. That trade is legitimate. It is not free.
Run it
The Yale endowment spending calculator is labelled on the page as a Yale / endowment spending calculator because that is the query. It blends last year’s inflation-indexed spend with a target percentage of assets. Compare it with Vanguard dynamic spending, which clamps a percent-of-balance target instead of averaging with last year. A rule that reads market valuations instead of last year’s spend is covered in the CAPE-based withdrawal guide.
When a household wants this
When a lumpy 10% Guyton cut would be a fight, and a pure percent-of-balance cheque would bounce too much to plan a year. When you can accept that a long bear will still grind spending down — just not in one step.