Cash flow for small businesses: how to forecast, plan for tax bills and get paid on time

Plenty of UK businesses that look healthy on paper still get into trouble because the money isn't in the bank when a bill falls due. Cash flow problems are rarely about a business being unviable. Usually they come down to timing: customers pay late, a tax bill lands in the same month as a big supplier invoice, or growth eats up cash faster than expected.

The good news is that cash flow is one of the most controllable parts of running a business. With a simple forecast, some discipline around tax and a firmer approach to invoicing, most owners can see problems coming weeks or months ahead.

Profit and cash are not the same thing

Profit is what your accounts say you earned over a period. Cash is what is actually in your account today. The two can drift a long way apart.

You might invoice £20,000 of work in March and record it as income, but if the customer pays on 60-day terms you won't see that money until May. Meanwhile you've already paid staff, rent and suppliers. Stock works the same way: money spent on goods sitting in a warehouse has left your account, but it only turns into profit when you sell.

This is why a growing business can feel permanently short of money. More sales often mean more cash tied up in unpaid invoices and stock before the income arrives.

Build a simple rolling cash flow forecast

A cash flow forecast doesn't need specialist software. A spreadsheet works well, and most cloud accounting packages include a forecasting tool.

A common approach is a rolling 13-week forecast, roughly one quarter, updated weekly. Short enough to be accurate, long enough to spot trouble.

• Start with your actual bank balance today, not what your accounts say.
• List expected money coming in each week, based on when customers realistically pay, not when invoices are due. If a client always pays two weeks late, forecast it that way.
• List money going out: wages, rent, loan repayments, supplier bills, subscriptions, insurance and, crucially, tax.
• Work out the closing balance for each week, which becomes the next week's opening balance.
• Look for the low points. Any week where the balance dips close to zero, or below your overdraft limit, needs action now, not when it arrives.

Each week, compare what actually happened with your forecast. Over time you'll learn which numbers you tend to be optimistic about, and the forecast will become more reliable.

Plan for the big tax bills

Tax is one of the most common causes of a cash crunch, because the bills are large and arrive in lumps. The fix is to treat money owed to HMRC as never really yours, and to set it aside as it comes in.

The main payment points to build into your forecast include:

• VAT: if you're VAT-registered and file quarterly, payment is generally due one calendar month and seven days after the end of the VAT period. Remember that the VAT you charge customers belongs to HMRC.
• PAYE and National Insurance: employers usually pay HMRC monthly, by the 22nd of the following month if paying electronically. Smaller employers may be able to pay quarterly.
• Corporation Tax: for most smaller limited companies, payment is due nine months and one day after the end of the accounting period, which is before the return itself is due.
• Self Assessment: sole traders and partners pay by 31 January after the end of the tax year, and many also make payments on account on 31 January and 31 July. The first year of payments on account can be a shock, because you may pay the previous year's balance plus an advance on the current year at the same time. Making Tax Digital for Income Tax, which began in April 2026 for sole traders and landlords with qualifying income over £50,000, adds quarterly updates to HMRC but does not change these payment dates.

Many owners open a separate savings account and transfer a fixed percentage of every payment received into it. Your accountant can help you set a sensible percentage based on your profits and structure. Rates and thresholds change at most Budgets, so check gov.uk for the figures that apply to the current tax year. For the basics of VAT registration and record-keeping, see our guide to small business bookkeeping and VAT.

If you can see you won't be able to pay a tax bill in full, contact HMRC before the deadline. It may be possible to agree a Time to Pay arrangement. Interest still runs on unpaid tax, at the Bank of England base rate plus 4%, and penalties can apply, but HMRC is generally more receptive to businesses that get in touch early.

Get paid faster

The quickest way to improve cash flow is usually to shorten the gap between doing the work and receiving the money.

• Agree payment terms in writing before you start. Put them in your contract or terms and conditions, not just on the invoice.
• Invoice immediately. Every day you delay sending an invoice is a day added to when you get paid.
• Make invoices easy to pay. Include your bank details, a clear due date, a purchase order number if the customer uses them, and the right contact name. Invoices are often paid late simply because they went to the wrong person.
• Offer simple payment options such as bank transfer, card or direct debit for regular customers.
• Ask for deposits or staged payments on larger or longer jobs, so you aren't funding the whole project yourself.
• Have a chasing routine. A polite reminder a few days before the due date, another on the day, and a firm follow-up shortly after. Accounting software can automate much of this.
• Check new customers before extending credit, particularly for large orders. A credit check or a look at a company's filing history on Companies House can be revealing.

Know your rights on late payment

Under the Late Payment of Commercial Debts (Interest) Act 1998, businesses can usually claim statutory interest on overdue invoices to other businesses, plus a fixed sum in compensation for recovery costs. The interest rate is set at 8% above the Bank of England base rate. The fixed compensation depends on the size of the debt: £40 for debts under £1,000, £70 for debts of £1,000 to £9,999.99, and £100 for debts of £10,000 or more. If a payment date hasn't been agreed, payment is generally treated as due 30 days after the customer receives the invoice or the goods or services.

Whether you use these rights is a commercial judgement: some owners hold back to protect a valued relationship. But simply mentioning statutory interest in your terms can encourage prompt payment.

Tougher rules are on the way. The Small Business Protections (Late Payments) Bill, introduced to Parliament in May 2026, would cap payment terms at 60 days when large businesses pay smaller suppliers, make statutory late payment interest mandatory so it can't be replaced by a lower contractual rate, and give the Small Business Commissioner new powers to investigate payment practices, adjudicate disputes and fine persistent late payers. The Bill is still going through Parliament and is not yet law, so check gov.uk for the latest position. In the meantime, the Office of the Small Business Commissioner can already help with some payment disputes between small businesses and larger customers.

Manage what goes out

Cash flow has two sides. Ways to keep more money in the business include:

• Negotiating longer terms with suppliers, especially those you've used reliably for a while.
• Reviewing subscriptions and direct debits regularly. Software, memberships and services that seemed useful a year ago can quietly add up.
• Keeping stock lean, ordering little and often where practical rather than tying up cash in bulk.
• Timing larger purchases for months when your forecast shows a healthier balance, or spreading the cost through leasing or hire purchase if it makes sense after comparing the total cost.

Build a buffer and line up finance early

Aim to build a cash reserve covering a few months of essential costs, such as wages, rent and key bills. It won't happen overnight, but even a small buffer gives you breathing space.

It's also worth arranging finance before you need it. Lenders tend to look more favourably on a business that applies from a position of strength. Options include an overdraft, a revolving credit facility or invoice finance, where a provider advances money against unpaid invoices. Each has costs and conditions, so compare them carefully and read the small print. The British Business Bank, a government-owned organisation, publishes general guidance on finance options for smaller firms.

Where to get help

An accountant can help you set up a forecast, estimate tax bills and spot warning signs. Gov.uk has official guidance on tax deadlines, late payment rights and dealing with HMRC. If you're worried that your business may not be able to pay its debts, take professional advice promptly, because directors of limited companies have legal duties once insolvency becomes a possibility.

This article reflects the rules as at 15 October 2026. It is general information only and is not financial, tax or legal advice. Rules and rates change, so check gov.uk or speak to a qualified professional about your circumstances.