How to build a 13-week cash flow forecast

Most owners know whether last year was profitable. Far fewer can say how much cash will be in the bank eight weeks from Friday. That gap is where trouble starts. A business can be profitable on paper and still miss a payroll, because customers pay late, a tax payment lands in the same week as a large supplier bill, or inventory soaks up cash before it turns into sales.

A 13-week cash flow forecast closes that gap. It is a simple, week-by-week view of the cash coming in, the cash going out and what is left at the end of each week. Thirteen weeks is one quarter: short enough to forecast with reasonable accuracy, long enough to see a problem in time to do something about it.

Why weekly, and why cash instead of profit

Your income statement records revenue when you earn it and expenses when you incur them. Your bank account only cares about when money actually moves. A big job invoiced in March may not be paid until May. Payroll goes out every other Friday no matter what. A monthly view blurs those timings together; a weekly view shows the low points, and the low points are what matter.

Step 1: Set up the frame

Open a spreadsheet. Put 13 week-ending dates across the top. Down the side, create three blocks: cash receipts, cash disbursements, and the cash summary. In the summary, each week has an opening balance, plus receipts, minus disbursements, equals the closing balance. Next week's opening balance is this week's closing balance. That one linked row is the backbone of the whole forecast.

Step 2: Start from the real bank balance

The opening balance in week one is the actual cash in your operating accounts today, not the number in your accounting system if it hasn't been reconciled. If you keep money in more than one account, decide which accounts count as available cash and stay consistent. A forecast that starts from the wrong number is wrong in every week after it.

Step 3: Forecast receipts

Begin with what you already know: your open receivables. Go through the aging report and place each invoice in the week you realistically expect to be paid, based on how that customer actually pays, not on the due date printed on the invoice. Then add sales you expect to make and collect within the 13 weeks, using your usual collection pattern. Keep other inflows, such as loan draws, owner contributions or asset sales, on their own lines so they are never mistaken for operating cash.

Step 4: Forecast disbursements

List every way cash leaves the business, on its own line, in the week it goes out:

• Payroll and payroll taxes, on your actual pay dates.
• Rent, leases, insurance, software and other fixed commitments.
• Supplier and subcontractor payments, from your open payables and expected purchases.
• Loan payments, credit card payments and interest.
• Sales tax, estimated income tax and other periodic payments that are easy to forget.
• Planned one-off spending: equipment, a vehicle, a deposit on new space.

Large, lumpy payments deserve the most care. They are rarely the biggest line over a year, but they are often the reason a single week goes negative.

Step 5: Set a minimum cash line

Decide the lowest balance you are comfortable holding, for example enough to cover one payroll plus the fixed bills that land with it. Add that number as a row and flag any week where the closing balance dips below it. This turns the forecast from a report into an early-warning system. When a week is flagged, you have options while there is still time: chase specific receivables, move a purchase, talk to a supplier about timing, or arrange a line of credit before you need it rather than after.

Step 6: Roll it forward every week

The forecast earns its keep through repetition. Pick one day each week. Replace last week's forecast with the actual receipts and payments from the bank, compare the two, and note the biggest differences. Then drop the finished week and add a new week 13. Over time, the variance notes teach you where your assumptions are off, such as a customer who always pays two weeks late or a cost that runs higher than you budgeted, and the forecast gets sharper.

What a good forecast gives you

Done consistently, a 13-week forecast changes how cash decisions get made. Hiring, buying equipment or taking on a large job stops being a gut call, because you can see what each choice does to your lowest week. Conversations with your banker get easier, because you can show exactly when and why you might need to borrow. And the Sunday-night worry about whether payroll will clear gets replaced by a number you trust.

You don't need special software to start. A clean spreadsheet, your bank balance, your aging reports and an hour a week will get you most of the way. Cloud tools can automate the bank feed and the roll-forward later, once the habit is in place.

General information for business owners, not advice for your specific situation. For tax or legal questions, talk to your CPA or attorney.