A 13-week cash flow forecast is a week-by-week map of money coming in and going out for the next quarter. It answers a blunt question: will there be enough cash in the bank on the worst week, not just on average?
Profit on a monthly management report can look fine while cash is about to dip. Payroll, VAT, supplier terms and slow debtors do not care that your P&L looked healthy last month. This guide is general information for UK small businesses. It is not regulated financial advice for your specific situation.
Cashwatch™ by Ask Alfred™ forecasts thirteen weeks out, ages every debtor, and drafts chase emails. It is built so tax bills and late invoices show up in the same view. Alfred prepares the picture. You decide what to do.
Why thirteen weeks
Thirteen weeks is long enough to see a VAT quarter, a payroll cycle, and a slow-paying customer land in the same window. It is short enough that your assumptions stay useful. A twelve-month annual budget is vital for planning. It is a poor early-warning system for next Tuesday's balance.
- Near enough to act: you can still chase invoices, delay a purchase, or talk to your bank.
- Far enough to matter: tax and rent spikes often sit four to ten weeks out.
- Weekly grain: monthly totals hide the week you go negative between inflows.
What to include in the forecast
Build from bank reality, not from hope. Start with today's cleared balance, then layer known movements week by week.
Opening bank balance for every account that pays the bills (including cards if they drain cash).
Customer receipts you can defend: due invoices, standing orders, known payment dates.
Supplier payments on their real terms, not when you wish they were due.
Payroll, pensions and contractor costs on the weeks they leave the account.
Tax: VAT, PAYE, corporation tax instalments, and any payment plans.
Rent, finance and subscriptions that hit on fixed dates.
One-offs: stock buys, deposits, refunds, director drawings you already plan.
Cash flow is not profit
Owners mix these up constantly. A simple split:
- Profit asks whether the business earned more than it spent in accounting terms.
- Cash asks whether the bank account can fund the next thirteen weeks of real payments.
You can be profitable and still run out of cash if customers pay late, you bought stock up front, or a tax bill lands before the related receipts. A 13-week forecast exists to catch that gap.
Build it in a sensible order
- Lock today's cash. Reconcile the bank so the opening figure is true.
- Lay out the calendar. Thirteen week-ending dates down the page or across columns.
- Add committed outflows first. Payroll, rent, finance, tax dates you already know.
- Add expected inflows with honesty. Weight late payers down, or put them in later weeks.
- Compute a closing balance each week. Watch the lowest point, not only the final week.
- Stress it. What if your biggest debtor slips two weeks? What if a supplier wants cash on delivery?
The tax-aware gap most forecasts miss
Many cash tools track sales and suppliers well and still surprise you with VAT or PAYE. UK small businesses live on tax calendars as much as customer calendars. A useful 13-week view includes:
- VAT return periods and the payment due after the period ends
- PAYE / NIC payment dates if you run payroll
- Corporation tax due dates or instalments your accountant has flagged
- Any HMRC payment plan already agreed
Ask Alfred™ is built around that combined view: cash, debtors and tax timing in one place through Cashwatch™, rather than a sales-only forecast that looks calm until HMRC day.
How to read the lowest point
The most important number is often the trough: the lowest weekly closing balance in the next thirteen weeks. On the Ask Alfred™ homepage, an illustrative Cashwatch™ card shows a lowest dip figure (for example £96,000) alongside chase emails ready. That figure is a product example, not your forecast.
If your trough is uncomfortably close to zero (or negative):
- Chase the invoices that move the needle (see How to chase unpaid invoices).
- Delay non-essential spend until after the trough week.
- Talk to your accountant early about tax timing, not the week before a payment is due.
- If you need external finance, start that conversation with a clear thirteen-week picture, not a vague worry.
Keep it alive, not perfect
A forecast that is updated weekly beats a beautiful spreadsheet you built once in January. Each week:
Roll the window forward one week and drop the week that just passed.
Replace guesses with actuals for receipts that landed or slipped.
Re-age debtors so late invoices do not stay marked as "due this week" forever.
Check next tax and payroll dates still sit in the right weeks.
Cashwatch™ is designed to keep that rhythm without a blank-sheet rebuild every Monday.
How this ties to year-end
Cash forecasting and year-end prep share the same raw materials: bank truth, aged debtors, and known tax dates. When you are closing a period, use the UK year-end accounts checklist for the accounts pack, and keep the thirteen-week view running so filing season does not starve the business of cash.
Want a blank thirteen-week grid you can print or save as a PDF? Use the printable 13-week cash flow template.
Quick 13-week checklist
- Start from a reconciled bank balance.
- Map thirteen weeks of inflows and outflows.
- Put tax and payroll on the real due weeks.
- Be honest about slow debtors.
- Watch the lowest weekly balance.
- Update every week and chase what moves cash.
What to read next
- Printable 13-week cash flow template
- Cash flow forecast template UK
- Cash flow forecasting that includes tax
- Cashwatch™ deep dive
- How to chase unpaid invoices
- UK year-end accounts checklist
- Making Tax Digital for Income Tax 2026
- Ask Alfred™ homepage
- All guides
This page is general information for UK small businesses. Nothing here is regulated financial advice, and nothing regulated should be submitted without a human approval from a qualified professional. Illustrative product figures are examples, not your cash forecast.