A 13-week cash flow forecast is the projection lenders ask for before extending credit: cash in minus cash out, week by week, ending balance every week. This kit builds that view from your own numbers. No macros; works in Excel 2007+ and Google Sheets. Cashflow13.xlsx has five tabs. Setup holds opening cash, the week-1 date, and your minimum cash line. A/R Aging turns each open invoice into an expected collection: bucket by age (current to 90+ days), a rate per bucket (90% current down to 5% past-90, all editable), and the week the money lands. Forecast runs 13 live week columns: collections flow in from the aging tab, you type bills and variable spending, and ending cash chains week to week. Any week that ends below your minimum turns red. Actual logs what really happened and computes variance per category and week. Lender-Summary prints one page: runway in weeks, weeks below minimum, lowest cash point, top 3 deficit drivers, and a line chart of ending cash. It is forward-looking planning, not historical bookkeeping: it answers "will I run out?", the question your books can't. The 10-page PDF guide covers the 15-minute fill-in order, calibrating collection rates from your own invoice history, why lenders standardize on 13 weeks, and five cash-crunch patterns to catch early.