How long you can operate before the bank account hits zero: cash on hand divided by monthly burn. For a DTC brand the naive version lies, because the biggest cash calls are lumpy inventory purchase orders, not smooth monthly costs - which is why the playbook's instrument is a 13-week rolling cash flow forecast, updated weekly, rather than a single runway number. Cash flow, not profit, is what kills DTC brands: a profitable P&L and an empty bank account can coexist for months. The mistake is confusing revenue with cash and discovering the gap the week a supplier deposit falls due.
Benchmark. Hold 90+ days of cash runway as a minimum. Run the 13-week rolling forecast weekly and fix any negative week the week you see it - the earlier a gap shows, the cheaper the solutions (supplier terms, financing, order timing) are.