FP&A

Building a 13-Week Cash Forecast

The single most useful financial tool for a small business. Not a budget, not a P&L — a weekly cash projection you actually use.

By Harry Prabandham3 min · 5 slidesUpdated May 3, 2026

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Annual budgets are too coarse — a great year on paper still goes broke in March if cash timing is wrong.
Monthly P&L looks backward — it tells you what happened, not what's coming.
13 weeks is a quarter of weekly granularity — short enough to forecast accurately, long enough to see oncoming problems.
Standard tool in turnaround and lender contexts because it's the format banks and creditors trust.
Run it weekly, refresh it weekly. A 13-week forecast updated quarterly is just a budget by another name.

Rows: cash sources (collections, deposits, financing) and cash uses (payroll, vendors, taxes, debt service, distributions, capex).
Columns: 13 weeks across the top, week starting Monday.
Bottom: opening cash balance, plus net cash flow per week, equals ending cash balance per week.
Track actual vs. forecast each week — variances tell you where your assumptions are wrong, not where to revise the future.

Collections from existing A/R: use historical DSO patterns, not invoice due dates. If customers pay net-45 on average, model net-45.
New sales collections: only count what's already in the pipeline with reasonable close probability — not aspirational.
Financing draws (lines of credit, factoring) — model what you actually plan to draw, not what's available.
Owner contributions, investor wires, and other one-time inflows by specific week.

Payroll: weekly or bi-weekly cadence, including employer taxes (multiply gross by ~1.10 for the true cash hit).
Vendor payments: schedule based on actual payment cadence (most operations pay vendors on net-30 from invoice, not from receipt).
Quarterly tax estimates (April, June, September, January) and payroll tax deposits.
Annual lump sums: insurance renewals, software annual renewals, year-end bonuses, equipment purchases.
Debt service: principal AND interest, in the actual week each is due.
Distributions to owners — easy to forget but real cash out the door.

Lowest projected weekly ending balance is your runway warning — if it goes below your minimum operating cash, act now.
Variance analysis (actual vs. forecast) each week reveals systemic forecasting errors: late collections, missed expenses, optimistic sales.
Use it to time decisions: a hire, a major purchase, a distribution — model the impact before committing.
Share it with your bank or board — it builds credibility and is what they want to see anyway.
Need help building one? Rubric Financial sets up the 13-week model and runs the weekly refresh as part of fractional CFO engagements.