A cash flow forecast is one of those phrases that sounds more complicated than it is. Strip it back and it is simply a week-by-week or month-by-month picture of when money is expected to arrive in your bank account, and when it is expected to leave. That timing - not your revenue, not your profit - is what determines whether your business survives its early years.
This guide walks you through what a cash flow forecast actually is, why profitable businesses still run out of cash, and how to build a minimum viable forecast this week - no accounting software required, no prior knowledge assumed.
What a Cash Flow Forecast Actually Is (and What It Is Not)
A cash flow forecast is a forward-looking document that records the money you expect to receive and the money you expect to pay out, period by period. The key word is expect. It is not a record of what has already happened - that is a bank statement or a profit and loss account. A forecast looks ahead so you can see problems before they arrive.
It is not a budget. A budget tells you what you plan to spend. A forecast tells you when cash will actually move. And it is not a profit and loss statement - we will come back to why that distinction matters, because it is the most costly mistake early-stage founders make.
Cash Flow Forecast - Defined
A cash flow forecast maps the actual dates money is expected to enter and leave your bank account. It covers all cash movements: customer receipts, supplier payments, tax obligations, wages, rent, loan repayments, and your own drawings.
A well-built forecast typically covers three to twelve months ahead, though the right horizon depends on your business - lenders often ask for a 13-week weekly view, while annual planning usually calls for a 12-month monthly model. For most early-stage businesses, a rolling three-month view is enough to catch the timing problems that cause real damage. You update it monthly - ideally weekly - as actuals come in.
Why Cash Flow Kills Profitable Businesses - and How a Forecast Helps
The businesses that go under are not always the ones losing money. Many fold while turning a profit on paper. The reason is almost always timing.
You complete a project in October. You invoice on completion. Your client has 30-day payment terms and pays on day 28. That money arrives in late November. But your supplier needed paying in October. Your PAYE liability for October is due to HMRC by 19 November. Your VAT quarter closes on 31 October and payment is due 7 December. And you need to take drawings to pay your own rent.
The profit is real. The cash gap is also real. A forecast makes that gap visible before it becomes a crisis. Improving cashflow should be a business core focus fro a small business.
The Tax Timing Problem
UK founders regularly underestimate HMRC timing. PAYE payments are due monthly by the 22nd (if paying electronically) or the 19th (if paying by cheque or post). If either date falls on a weekend or bank holiday, payment must clear by the last working day before it.
VAT is due one month and seven days after each quarter end (for businesses on the standard, flat rate, or cash accounting schemes). Businesses on the Annual Accounting Scheme follow different rules - check your HMRC VAT account for your specific deadlines.
Corporation Tax is due nine months and one day after your company's year end - but this applies to companies with annual profits of £1.5 million or less. If your profits exceed £1.5 million, you must pay by quarterly instalments instead. Check HMRC's guidance for the instalment deadlines relevant to your company size. None of these dates align with your invoice schedule - and missing them triggers penalties.
A cash flow forecast does not prevent these obligations. It makes sure you have the cash set aside when they fall due - and tells you in advance if you will not.
The Difference Between Cash Flow and Profit (and Why It Matters More Than You Think)
Profit is what you have earned minus what it cost you to earn it. Cash flow is what is actually in your bank account. These two numbers are not the same, and they are rarely in the same place at the same time.
When you raise an invoice, your profit and loss account records it as income immediately - even if the client has not paid yet. Your bank balance, on the other hand, does not move until the money arrives. In UK accounting, this is called the difference between accruals accounting (recording income and costs when they are earned or incurred) and cash accounting (recording when cash actually moves).
Your cash flow forecast works on cash dates only. It does not care when you raised the invoice. It cares when the money lands.
Illustrative Example
Based on a common UK founder scenario, not a specific documented case:
A freelance web developer invoices £4,000 on 1 October. Her profit and loss shows a profitable month. But her client pays on 60-day terms, so the money arrives in early December. Meanwhile, she owes her accountant in October, has a VAT payment due in November, and needs drawings each month. Her bank balance tells a very different story to her profit and loss - and without a forecast, she would not have seen the November shortfall coming.
Important note: 60-day payment terms for freelancers are at the upper limit of what the UK's new late-payment reforms treat as acceptable. As of March 2026, the government announced a 60-day statutory cap on B2B payment terms (pending primary legislation), and the Fair Payment Code - which replaced the Prompt Payment Code in January 2025 - actively encourages 30-day terms for small business suppliers.
The Four Numbers You Need to Start Your First Forecast
You do not need a complete picture to start. Most early-stage founders can build a useful forecast from four categories of information.
Opening balance. The actual cash in your business bank account today. This is your starting point - not your theoretical profit, not your invoiced revenue. Your real bank balance.
Expected cash in. The dates you realistically expect money to arrive. For each outstanding invoice, this means the date the client is likely to pay - not when you raised the invoice. For recurring revenue, it means the expected payment date. Be honest here. Optimism is the enemy of a useful forecast.
Expected cash out. Every payment you will need to make, by date. This includes suppliers, rent, software subscriptions, wages or subcontractor costs, your own drawings, loan repayments, and all HMRC obligations - PAYE, VAT, and Corporation Tax or Self Assessment payments on account.
Closing balance. What is left at the end of each period. This is calculated automatically once you have the first three: opening balance plus cash in, minus cash out. A negative closing balance means you will run out of cash in that period.
That is the whole structure. Everything else - categories, colour coding, variance analysis - is refinement you can add later. Start with these four.
How to Build a Simple Cash Flow Forecast Step by Step
A spreadsheet with three months of columns is enough to get started. Here is the process, in order.
Building Your First Cash Flow Forecast
Set up your columns
Create one column per month (or per week if your cash flow is volatile). Add a row for each item. Label the first column 'Opening Balance'. Your last row in each column will be the Closing Balance, which becomes the Opening Balance for the next period.
Enter your opening balance
Use your actual bank balance today - the figure on your business account statement. Do not estimate. This anchor point is the only number in your forecast that is certain, so it must be exact.
List all expected income by receipt date
Go through every outstanding invoice and expected payment. For each one, enter the cash in the month you realistically expect it to land. If a client is slow to pay, reflect that - do not record it in the invoice month. If you are VAT-registered, record the net amount only (VAT collected from clients goes to HMRC, not to you).
List all expected outgoings by payment date
Enter every payment you will need to make, in the month it falls due. Include: supplier invoices, rent or mortgage, any wages or subcontractor payments, software and subscriptions, loan repayments, your own drawings, PAYE (due by 19th of the following month), VAT (due one month and seven days after your quarter end), and any Corporation Tax or Self Assessment payments on account you know are coming.
Calculate your closing balance
For each month: Opening Balance + Total Cash In - Total Cash Out = Closing Balance. Carry this figure forward as the next month's Opening Balance. Any month showing a negative closing balance is a danger period you now have time to address.
Update it regularly
A forecast only stays useful if you maintain it. Once a week, update actual receipts and payments. Where actuals differ from your forecast, understand why - and adjust your forward projections accordingly. The discipline of maintaining it is where the real value comes from.
With your forecast built, the next step is knowing how to read it. A completed spreadsheet full of numbers is only useful if you can identify which signals require action - and which levers you can pull in response.
Reading Your Forecast: What to Look For and What to Do About It
Once built, your forecast is only useful if you know what to act on. There are three signals worth looking for.
A negative closing balance in any month. This is your most urgent signal. It means your projected outgoings exceed your projected income plus opening balance. You need to either bring income forward (chase invoices earlier, ask for deposits, negotiate shorter payment terms), push costs back where possible, or arrange a short-term credit facility in advance - not in the middle of a crisis.
A closing balance that is consistently low. Not negative, but uncomfortably thin. This means you have no buffer against a late payment or an unexpected cost. As a general starting point, most early-stage businesses are advised to maintain at least three months of operating costs as a minimum cash reserve - and up to six months if revenue is seasonal or unpredictable - though your ideal buffer will depend on how predictable your income is and how quickly you can cut variable costs if needed.
Large movements in a single period. A big tax payment, a large supplier invoice, or a seasonal dip in revenue can produce a spike in outgoings or a trough in income. Spotting these in your forecast gives you time to smooth them - by setting cash aside in the preceding months, or by timing discretionary spending differently.
Chase Invoices Proactively
If your forecast shows a tight month ahead, the most effective lever is often invoice chasing. Consider sending a polite reminder a few days before payment is due - commonly five to seven days - rather than waiting until after the invoice is overdue.
Adjust the timing to suit your client relationships and payment terms.Many late payments are not deliberate; they are simply forgotten. A brief, professional chase email before the due date costs nothing and consistently accelerates receipts.
Common Cash Flow Forecast Mistakes UK Founders Make
The mechanics of a forecast are straightforward. The errors are almost always in the assumptions.
Recording income on the invoice date rather than the expected payment date. This is the most common mistake and the most dangerous. Your forecast must reflect when cash arrives, not when you raised the invoice.
Forgetting HMRC obligations entirely. Self Assessment payments on account, VAT returns, and PAYE settlements are not optional and are not small. If they are not in your forecast, your closing balances are meaningless.
Assuming best-case payment terms. If a client has a history of paying late, forecast accordingly. Building your cash plan on optimistic assumptions sets you up for a shortfall that was entirely predictable.
Not including your own drawings. Sole traders and limited company directors who pay themselves via dividends or drawings often omit these. They are a real cash outflow and must be included.
Including VAT in income figures. If you are VAT-registered, the VAT element of your invoice is collected on behalf of HMRC - it is not your revenue. Record income net of VAT, and show the VAT payment to HMRC separately in your outgoings at the correct quarter-end date.
The Optimism Trap
Founders routinely build forecasts that reflect the business they hope to run, not the business they actually run. If your income projections consistently rely on new clients converting quickly or existing clients paying on time, you are building a plan that will fail on contact with reality.
Run a conservative scenario alongside your base case. It is uncomfortable - and it is the version that keeps you solvent. Ask your accountant or bookkeeper to review your cash flow forecast; their perspective will likely be different.
When to Use a Spreadsheet vs Accounting Software for Your Forecast
For most early-stage founders, a spreadsheet is the right starting point. It forces you to understand every line of your forecast, which is valuable in itself. Google Sheets or Excel are both fine. BGE offers a cash flow forecast template as a free download if you want a working starting point rather than a blank sheet.
Accounting software becomes genuinely useful when your transaction volume grows, when you have staff on payroll, or when your VAT returns are complex enough that maintaining a separate manual spreadsheet creates real reconciliation work.
At that point, Tools like Xero or QuickBooks connect to your accounts and can surface actuals, but pulling them automatically into a rolling forecast usually requires a dedicated add-on such as Float or Fathom. Once set up, these integrations can save meaningful time each month.
The honest answer is: use whichever tool you will actually maintain. A spreadsheet you update weekly is worth more than accounting software you log into quarterly.
The Tool Is Not the Point
The value of a cash flow forecast is not in the software or the template. It is in the discipline of thinking concretely about when money moves. Even a rough forecast built in 30 minutes on a plain spreadsheet will reveal timing problems that would otherwise catch you off guard. Start simple. Refine as you go.
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