The Miller-Orr cash management model37 is a useful frame, but it is the wrong tool when applied to the whole household cash flow. The fundamental assumption is that cash flows are stochastic — a zero-drift random walk. Household cash flows are largely deterministic: rent on the first, utilities on the fifth, salary on the fifteenth and thirtieth, three credit-card autopays on known dates. Treating these structured events as random variability inflates the variance and produces an absurd target balance. The fix is to apply the model only to the residual unpredictable component, with the deterministic recurring layer handled by the cash-flow calendar and the known lumps pre-funded with the sinking fund described in section “Sizing the Fund”.