13-Week Cash Flow Forecast: How to Build a Rolling Forecast in Excel

A 13-week cash flow forecast shows, week by week, how much cash a business expects to receive and pay over the next quarter, and what its bank balance will be at the end of each week. This guide explains when to use one, the information you need, a step-by-step method and a complete worked example you can check line by line.

What is a 13-week cash flow forecast?

It is a short-term, direct-method cash forecast: you list the actual cash you expect to come in (customer payments, cash sales, loans received) and go out (suppliers, payroll, rent, tax, loan repayments) in the week you expect each one to happen. Thirteen weeks is one quarter — long enough to see trouble coming and act on it, and short enough that most of the receipts and payments are already known from invoices, bills, payroll and contracts.

The forecast is rolling: each week you replace the week just finished with actual figures, check what went differently, and add a new week at the end, so it always looks 13 weeks ahead.

When a business should use one

• Cash is tight, or one large payment (payroll, a tax bill, a loan instalment) could take the account below a safe level.
• Sales are seasonal or growing fast, so cash arrives later than the costs of delivering the work.
• You depend on a few large customers whose payment timing matters.
• A bank, lender or investor has asked for a short-term cash forecast.
• You are deciding whether you can afford a purchase, a hire or a delay in collecting a debt.

A monthly forecast can hide the problem: payroll, rent and a tax payment can all fall in the same week, and a month-end balance that looks comfortable can mask a week in the middle that does not.

Cash flow forecasting vs profit forecasting

A profit forecast (a forecast income statement) records revenue when it is earned and expenses when they are incurred — the accruals basis. A cash flow forecast records money only when it actually moves in or out of the bank. The two can tell very different stories:

• Credit sales: an invoice for 10,000 issued in week 1 on 30-day terms is revenue in week 1, but cash in around week 5 — later if the customer pays late.
• Non-cash expenses: depreciation reduces profit but is not a payment, so it never appears in a cash forecast.
• Loan repayments: the principal part of a loan repayment is a cash payment but not an expense in the profit forecast.
• Sales tax or VAT: tax you collect from customers is cash in, and the payment to the tax authority is cash out, even though neither is your revenue or expense.
• Stock purchases: paying for inventory uses cash immediately, but the cost reaches the profit forecast only when the goods are sold.

That is why a profitable business can still run out of cash. The 13-week forecast answers a different question from the profit forecast: will we have enough cash to pay what is due, every week?

Information you need

• Opening cash: today’s actual bank balance (all operating accounts), taken from the bank, not the accounting system.
• Open customer invoices (accounts receivable): amount, due date and, where you know it, the date you realistically expect payment.
• Expected new sales not yet invoiced, and when that cash should arrive — including cash or card sales.
• Unpaid supplier bills (accounts payable) and when you plan to pay them.
• Recurring payments: payroll and payroll taxes, rent, utilities, subscriptions, insurance — with their actual payment dates.
• Financing and one-off items: loan repayments, interest, tax payments, equipment purchases, owner drawings, any funding expected.
• Minimum cash floor: the lowest balance you are willing to hold, plus any agreed overdraft facility.

Your accounts receivable aging report and accounts payable list are the backbone of the first few weeks; recurring items and sales estimates fill in the later weeks.

How to build a 13-week cash flow forecast, step by step

1. Set up 13 weekly columns. Choose a fixed week-start day (for example Monday) and label each week with its start date.
2. Enter opening cash for week 1 from the actual bank balance.
3. Place every receipt in the week you expect the cash. Start from open invoices. Use each customer’s real payment behaviour, not just the due date: if a customer usually pays 10 days late, place their invoices 10 days after the due date. Then add uninvoiced sales and cash sales.
4. Place every payment in the week it will leave the bank. Supplier bills by planned payment date; payroll on pay dates; rent, loan and tax payments on their scheduled dates; then other operating costs.
5. Calculate each week:
   Total receipts − Total payments = Net cash flow
   Opening cash + Net cash flow = Closing cash
   Closing cash of week n = Opening cash of week n+1
6. Compare each closing balance with your minimum cash floor. Headroom = Closing cash − Minimum cash floor. Any negative headroom is a week that needs action.
7. Stress-test it. Push receipts a week later, or cut uninvoiced sales by a percentage, and see whether the lowest week still holds.
8. Decide and act on any week below the floor: chase specific invoices, move a supplier payment, delay a purchase, or arrange funding in advance.

Worked example: a 13-week forecast for a small distributor

The figures below are for a fictional small wholesale business, used only to illustrate the method. It starts with 38,000 in the bank and wants to keep at least 15,000 (its minimum cash floor). Payroll of 14,000 is paid every two weeks, rent of 6,000 roughly every four weeks, a loan instalment of 2,500 every four weeks, and a sales tax payment of 9,500 falls due in week 6. In week 6, one customer invoice of 4,000 that was due is expected to be paid a week late, in week 7.

How week 1 is calculated

Week 6: the problem week

The business is not out of cash in week 6, but it would drop 1,500 below the level it wants to keep, in the same week that payroll and the tax payment fall due.

What the forecast tells this business

• Lowest balance: 13,500 in week 6 — the only week below the 15,000 floor.
• Thin weeks: weeks 8 and 10 close with only 2,500 and 3,000 of headroom, both payroll weeks. Any further late receipt in those weeks would breach the floor.
• Over the quarter cash falls by 8,700, from 38,000 to 29,300: payments of 274,000 exceed receipts of 265,300. That trend is worth understanding even though no week goes negative.

Updating the forecast every week

1. Close the week. Record what was actually received and paid in the week just finished.
2. Compare with the forecast. Suppose week 1 actually brought in 19,200 (forecast 20,500) and paid out 17,300 (forecast 17,000). Actual closing cash is 38,000 + 19,200 − 17,300 = 39,900, which is 1,600 below the forecast 41,500. Find out why: a late customer, an unplanned payment, or a timing difference that will reverse next week.
3. Re-anchor to the bank. Start the new forecast from the actual bank balance (39,900), not from the old forecast figure.
4. Move the uncollected items. Anything that did not arrive goes into the week you now expect it — never just deleted.
5. Roll forward. Drop the finished week and add a new week 13, so you always see a full quarter ahead.

Handling uncertain receipts and payment dates

• Use expected dates, not due dates, for customers with a history of paying late.
• Be cautious with receipts and complete with payments. If you are unsure when a receipt will arrive, place it later; if you are unsure when a payment is due, place it earlier.
• Keep uninvoiced sales separate from invoiced receipts so you can see how much of the forecast depends on sales not yet made.
• Run a downside case: for example, all receipts 7 days later, or uninvoiced sales 20% lower. If the lowest week survives the downside case, the plan is robust.
• Do not hide disputes. A disputed invoice should not sit in the forecast at its due date; move it out or to the date you realistically expect a settlement.

Common mistakes and practical checks

Checks to run every week

• Week 1 opening cash equals the actual bank balance.
• Each week’s opening cash equals the previous week’s closing cash.
• Opening cash + total receipts − total payments for all 13 weeks equals week 13 closing cash.
• Every open customer invoice and supplier bill appears in exactly one week (or is deliberately excluded with a reason).
• Payroll and other recurring payments appear on every pay date in the 13 weeks.
• The lowest closing balance, the week it happens and the headroom against your floor are clearly visible.

To check the bigger picture behind the weekly numbers — whether current assets comfortably cover current liabilities — use the free Working Capital Calculator. A falling current ratio is often the early sign that a 13-week cash forecast is needed.

Frequently asked questions

Related resources

• Accounts Receivable Aging Report — how to monitor overdue customer invoices and see when cash is likely to be collected.
• Bank Reconciliation guide — how to verify bank transactions and keep your cash records accurate.

This guide is general information, not financial, accounting or legal advice. The worked example uses fictional figures. Written and reviewed by Ghayas Uddin, MS (Finance), financial analyst. Last reviewed 14 October 2026. Found an error? Email support@babadigit.com.