cashflow
13-Week Cash Flow Forecast
Rolling 13-week schedule of cash in and cash out. The single most important operating spreadsheet.
Definition
A 13-week cash flow forecast lists, week by week, every expected cash inflow and outflow, plus the running balance. 13 weeks (~one quarter) is long enough to see seasonality and short enough to remain accurate. The format used by every disciplined operator: two columns per week (cash in / cash out), running balance row, updated every Monday before email. Inflows should be conservative (assume late payers); outflows should be comprehensive (every recurring subscription, payroll run, sales tax remittance).
Building the model from scratch
Start with a Google Sheet, 14 columns wide: one for line item labels and 13 for the next 13 weeks beginning Monday this week. Three sections vertically: opening cash balance, cash in by source (each major client, plus aggregated small clients, plus other income), cash out by category (payroll, rent, contractors, SaaS, sales tax, owner draws, debt service, other). Bottom rows: net change for the week, ending cash balance. Pre-populate every recurring known outflow (rent, payroll, software subscriptions). Add expected inflows based on signed contracts and invoiced AR with payment terms applied. The first build takes 2 to 3 hours; weekly updates take 15 to 30 minutes.
Conservative inflow assumptions
The single biggest mistake US founders make is optimistic inflow forecasting. Rules to encode. One, count signed contracts only, not verbal commitments or sent proposals. Two, apply realistic payment timing: net-30 means cash arrives week 5 or 6 from invoice, not week 4. Three, discount large outstanding invoices by historical collection rate (if 15 percent of invoices go past 60 days, discount the model accordingly). Four, never count one-time large deals at full value until cash has cleared the bank. Five, exclude any income source you have not received before. The model should err 10 to 20 percent below actual; if it consistently overshoots, your assumptions are still too optimistic.
Comprehensive outflow tracking
Outflows are where forecasts miss because small subscriptions and quarterly bills get forgotten. Pull every bank and credit card statement from the last 90 days and list every outflow. Annualize quarterly and semi-annual bills (insurance, state filing fees, accountant retainers) into the weeks they hit. Include estimated tax payments (April 15, June 15, September 15, January 15 for US federal). Include sales tax remittances (monthly in most states for businesses over a threshold). Include payroll tax deposits (federal 941 deposits semiweekly or monthly depending on size). Include credit card and loan principal payments. Missing one major recurring outflow is what creates surprise crunches.
Using the model to make decisions
A 13-week cash forecast is not just a tracking tool; it is a decision tool. Before any major spend or hire, model the cash impact across the next 13 weeks. A 100K per year hire is roughly 2K per week loaded with taxes and benefits; that 2K must come out of every week starting week 4. If that drops ending cash below the safety threshold in any week, the hire is too early or salary needs adjusting. Same logic for marketing campaigns, equipment purchases, and contractor engagements. The forecast turns abstract decisions into specific weekly impact and prevents the slow-motion cash erosion that kills profitable businesses.
FAQ
Why 13 weeks and not a different horizon?
Thirteen weeks equals roughly one calendar quarter, which is long enough to capture seasonality (quarterly tax payments, annual insurance renewals, seasonal revenue patterns) and short enough to stay accurate. Beyond 13 weeks, forecasting accuracy drops sharply because customer behavior and unexpected expenses dominate. Inside 13 weeks, signed contracts and known recurring bills explain 80 to 90 percent of the cash movement, making the forecast actionable. The 13-week standard is used by virtually every restructuring firm, PE operating partner, and CFO in US small business.
How often should the forecast be updated?
Weekly, every Monday morning before anything else. The update workflow: pull latest bank balance (the new starting point), drop off last week from the front of the model, add a new week 13 at the end, update inflow expectations based on what actually collected versus what was forecast, update outflow expectations based on new known bills. The full update takes 15 to 30 minutes once the model is set up. During a tight period (under 8 weeks of runway), update daily and review with a partner or coach.
Should I model multiple scenarios?
For under 1M revenue, one realistic forecast is sufficient. For 1M to 10M, build three scenarios: base case (most likely), downside (largest customer leaves, AR slow by 30 days), and upside (current pipeline closes at expected win rate). Compare ending cash balance in each scenario at week 13. If downside drops below 1 month of OpEx, identify which expenses get cut and when. Documented scenarios beat mental models because they force specificity and create accountability.
What software replaces a Google Sheet?
For US small businesses, dedicated tools include Float, Pulse, Cashflow Frog, Fathom, and Jirav. They integrate with QuickBooks Online or Xero and pull actuals automatically, leaving the founder to maintain forecast assumptions. The catch: automation can hide judgment. The discipline of weekly manual review forces the founder to think about each customer and bill, which generates insight a dashboard never produces. Use the tool for visualization and historical accuracy, but keep the weekly Monday review ritual regardless of tooling.
What is the relationship between 13-week cash flow and the cash flow statement?
The 13-week cash flow is a forward-looking operational tool. The GAAP cash flow statement (operating, investing, financing) is a backward-looking financial report. Both matter, but for different purposes. The 13-week forecast guides daily operating decisions; the cash flow statement supports tax filing, investor reporting, and lender compliance. The 13-week model usually shows only operating cash flow plus debt service and owner draws (the items that move week to week); CapEx and financing activities show up as discrete events when they happen.
In your business
- →Update Monday morning before doing anything else
- →Be conservative on cash IN, comprehensive on cash OUT
- →Use it to make hiring, pricing, and marketing-spend decisions - not just to track