Plenty of profitable businesses run out of cash. The reason is timing: you pay suppliers, wages and tax before customers pay you. A cash flow forecast is a simple plan that shows how much money you expect to have in the bank in the coming weeks and months, so you can spot a shortfall early and act. This guide shows how to build one in a spreadsheet, step by step, with no accounting background required.
Cash flow versus profit
Profit is what is left after costs are deducted from sales over a period. Cash flow is the actual movement of money in and out of your bank account. You can make a profit on paper while having no cash, for instance if a big invoice is unpaid for 60 days while rent and wages are due this week. Late payment is a common problem for small firms, which is why forecasting cash, not just profit, matters.
What you need before you start
Gather your recent bank statements, your list of unpaid invoices, your regular bills and subscriptions, and any known upcoming costs such as insurance renewals, equipment, tax payments and holidays. If you keep tidy records, this takes minutes; our guide to bookkeeping for a small business explains how to do that. Decide your time frame. Twelve weeks is a good horizon for a new forecast, and many businesses also keep a rolling twelve-month view.
Step 1: Set up your spreadsheet
Create columns for each week or month. Add rows in three blocks: money coming in, money going out, and a summary. Start with an opening balance, which is the real amount in your bank account at the start of the first period.
Step 2: List your cash coming in
Record the money you expect to receive and, importantly, when you expect it, not when you invoice. If a customer normally pays 30 days after the invoice, enter the payment a month later. Include sales, deposits, grants, loan drawdowns and any personal money you plan to add. Be cautious: use the amounts you are fairly confident about, and check your payment history to see how late customers really are. Overestimating income is the most common forecasting mistake.
Step 3: List your cash going out
Add all regular payments: rent, utilities, software subscriptions, insurance, wages, loan repayments and supplier bills. Then add the irregular ones, such as annual insurance, equipment, accountant fees and marketing campaigns. For tax, include the dates when payments fall due. Self-employed people often face Self Assessment payments in January and July, and VAT-registered firms have quarterly returns, so check HMRC’s current rules and dates. We are not licensed tax advisers, so confirm the details for your situation with HMRC or an accountant.
Step 4: Calculate the net and closing balance
For each period, subtract total money out from total money in. That gives your net cash flow. Add it to the opening balance to get the closing balance, which becomes the next period’s opening balance. A simple formula in a spreadsheet will do this automatically, so you only need to update the numbers.
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Step 5: Look for the pinch points
Scan the closing balance row. Any week where it drops near or below zero is a warning. The earlier you spot it, the more options you have. Pinch points often appear when a large bill lands just before a large payment arrives.
How to fix a cash shortfall
If your forecast shows trouble, you have several levers. You can invoice sooner and more promptly, ask for deposits or part-payment upfront, and shorten your payment terms. You can chase overdue invoices politely but firmly; our guide to writing business emails that get replies includes useful tips for reminders. You can negotiate longer terms with suppliers, delay non-essential spending, or review pricing; see our article on pricing your services if margins are thin. If you need finance, compare options carefully and read the terms, and consider speaking to an authorised adviser, since we cannot give personalised financial advice.
Keep it up to date
A forecast is only useful if you update it. Once a week, replace forecast numbers with actual figures and extend the forecast by another week. Compare what happened with what you expected. Over time you will learn how long customers really take to pay and how accurate your estimates are. Build in a safety margin, for example by assuming some invoices arrive later than promised.
Common mistakes to avoid
Forecasting sales when invoiced instead of when paid, forgetting tax bills, ignoring seasonal dips, and never revisiting the forecast are the usual traps. Another is treating a bank balance as spendable money when part of it is owed to HMRC or suppliers. Keeping a separate savings pot for tax can prevent that.
Final thoughts
A basic cash flow forecast takes an hour to build and a few minutes a week to maintain, yet it can mean the difference between calmly handling a quiet month and scrambling to pay bills. Start simple, be honest about timing and review it regularly. This article is general information, not financial or tax advice; for decisions about borrowing, tax or your specific position, speak to a qualified adviser.
