The teaching formula
A common CAPE heuristic for a first-year withdrawal is 1.5% plus half the earnings yield, and the earnings yield is 1 / CAPE. At a CAPE of 20 that is 1.5% + 2.5% = 4%. Later years inflate that first-year dollar amount, so after year one it behaves like a fixed-real rule with a valuation-aware start.
Early Retirement Now’s papers use related but more elaborate mappings. This site’s calculator is the transparent one-line version so you can see the knob move. It is not a forecast of the next decade’s return.
Run it
The CAPE-based withdrawal calculator is the identity. Pair it with the safe withdrawal rate calculator at a fixed 4% to see what the CAPE start changed in year one. Both are on the nine-rule hub.
What it is not
It does not say stocks are cheap or expensive as advice. It does not time the market. It sets a starting cheque from a public valuation measure, then inflates that cheque. If you want spending to react later, use rails or Vanguard’s clamp, not a one-time CAPE look.