How do I build a 13-week cash flow forecast for my medical practice?

The 13-week window is chosen because it is long enough to see most insurance reimbursement lag (Medicare contractors cannot pay a clean electronic claim until a 13-day waiting period has passed and must pay clean claims within 30 days; commercial timing follows state prompt-pay laws; denials and rework extend the tail) and short enough to model accurately. Beyond 13 weeks, weekly granularity stops being useful and monthly forecasts take over. To build one for a medical practice, start with cash receipts. Map expected weekly collections by payer source: Medicare, Medicaid, each major commercial payer, and patient responsibility. Use your billing system's expected reimbursement on submitted claims, adjusted for your historical realization rate (as a reference point, HFMA puts a healthy net collection rate at 95 percent at minimum and 97 to 99 percent at best). Add scheduled patient copays and point-of-service collections based on visit volume on the schedule. For new claims, project based on visit volume forecasts and your average days-to-payment by payer. Then map cash disbursements. Payroll runs on a fixed cadence (typically biweekly). Rent is monthly. State and federal payroll tax deposits run on a fixed calendar (semi-weekly or monthly depending on lookback period). Quarterly estimated tax payments hit on April 15, June 15, September 15, and January 15. Debt service runs on the loan amortization schedule. Variable expenses (medical supplies, lab fees, billing service fees) follow patient volume. Insurance premiums, software subscriptions, and other operating expenses run on their own contract calendars. Each week, you replace the forecasted column with actuals, roll the window forward, and add a new week 13 at the end. Variance between forecast and actual reveals the assumptions that need fixing: realization rate too high, denial rate underestimated, patient AR overstated, and so on. The forecast is wrong every week; its job is early warning. A 13-week forecast that flags a $40K shortfall in week 8 gives you 7 weeks to draw from a working capital line, defer non-essential spend, accelerate collections, or restructure debt. The same shortfall surfacing as a missed payroll in week 8 is a crisis. The first version is usually rough but immediately useful, and by the third or fourth iteration it tends to become the report owners check first.