How to build a 13-week cash flow forecast (the direct method)

The 13-week cash flow forecast is the most useful single artifact in a small business's finance toolkit. It tells you, week by week, how much cash you'll have on hand — and the first week you might not.

Why 13 weeks?

A quarter is the right horizon for tactical decisions: hiring, financing, big AP runs, capex. Anything shorter misses second-order effects of collections slippage. Anything longer turns into a budget, which is a different exercise.

The direct method

The direct method schedules actual expected cash receipts and disbursements into the week they'll hit your bank account. That's different from indirect, which starts from net income and adjusts. For tactical planning, direct wins: it ties every dollar to a concrete invoice or bill.

Step 1: Inflows

Pull every open invoice. For each, schedule the expected payment date using the customer's historical days-to-pay (or DueDate if you have no history). Sum by week. That's your weekly AR row.

Step 2: Outflows

Pull every open bill. Schedule each one into the week of its due date. Add recurring outflows — payroll, rent, utilities, insurance — based on the trailing-90-day P&L run rate.

Step 3: Starting position

Sum every bank account balance. That's your week-zero starting cash.

Step 4: Roll

Each week's ending balance is the prior week's ending plus this week's inflows minus this week's outflows. Carry forward for 13 weeks.

What to look at

The first week your ending balance dips below your minimum cash threshold
The first week (if any) your ending balance goes negative
The trajectory: is cash building or eroding over the quarter?

What to scenario

The point of the model isn't the baseline — it's how robust your cash position is to surprises. Run these three:

Collections slip by 20%
Payables get stretched by 14 days
You hire one more person at $X/month

FlowCast does all of the above automatically from your QuickBooks data, and lets you drag the scenario sliders to see the impact live.