Principle 11 — Own it, don't rent it. Park the lifetime money in Treasuries, spend only the yield on maintenance.
| Lifetime price | |
| Interest per year (principal untouched) | |
| Interest as % of annual price | |
| Serving cost per year | |
| Fund lasts |
Math: interest per year = lifetime price × yield. The tier funds itself forever when serving cost ≤ multiple × yield (at the defaults: 5 × 3% = 15% of the annual price). Above that line the fund still degrades gracefully — draw = cost, growth = yield, solved exactly. Everything runs on this page; no server, no tracking, works offline once loaded.