Late payment is already one of the biggest day-to-day pressures for UK small and medium-sized enterprises (SMEs). The Longitudinal Small Business Survey found that 51% of businesses with no employees that offer trade credit say late payment is a problem, up from 2023. Add to that HMRC’s tougher late-payment interest rules, and the cost of a short cash squeeze can snowball faster than many owners expect. That’s why protecting cashflow has become as much about tax timing as it is about sales and debt control.
Since 1 January 2023, VAT late-payment interest has been charged from the first day a payment is overdue, calculated daily until it is cleared (HMRC, 2025). In April 2025, HMRC aligned the late-payment interest calculation across VAT and most other taxes at Bank of England base rate plus 4% (HMRC, 2025). With the late-payment interest rate sitting at 8% from 27 August 2025, even a brief delay now creates a noticeable cost.
In practice, this is not just about late payers. It can affect profitable businesses that hit a timing mismatch, a slow-paying customer or an unexpected VAT bill. In this article, we’ll explain what’s changed, how daily interest works and what we can do together to keep protecting cashflow while staying on the right side of HMRC.
What has changed, and why it matters for protecting cashflow
HMRC has moved away from older penalty styles, like the old VAT default surcharge, to a clearer split between penalties and interest. Interest is now purely a cost of being late, not a punishment for repeated lateness. That sounds fair, but it also means there’s no grace period.
Here are the key points to be aware of.
- Daily accrual from day one: VAT late-payment interest starts the day after the due date and runs until the debt is paid in full.
- Alignment across taxes: From 6 April 2025, late-payment interest for VAT, income tax, Class 4 national insurance contributions (NIC), capital gains tax (CGT) and most other regimes uses the same base-rate-plus-4% formula.
- Higher rates than recent years: With base rates higher than the low-rate era, the “background” cost of lateness is now material. HMRC updates the percentage when the Bank of England moves, so the figure can change during the year.
For SMEs, the big shift is speed. Previously, you might have had time to resolve a short shortfall before charges kicked in. Now, every day counts. Protecting cashflow means planning for tax outflows as actively as we plan for payroll or supplier runs.
How daily interest works in real life
Interest is calculated like a simple daily charge. HMRC applies the annual rate to the outstanding balance, then divides it by 365.
Say your VAT bill is £20,000 and you pay it 10 days late. At an 8% annual interest rate: £20,000 × 8% × 10 ÷ 365 = about £43.84 interest. That does not sound huge, but two things make it bite.
- Larger bills, especially VAT and corporation tax, drive up the cost quickly.
- Interest runs alongside penalties where those apply, so the total cost can stack up. And from 1 April 2027, the government has confirmed that penalties for late payment of income tax self assessment and VAT will increase, which makes getting ahead of problems even more important.
If a £75,000 corporation tax payment slips by a month, you’re looking at roughly: £75,000 × 8% × 30 ÷ 365 = about £493.
That is almost £500 for a timing issue, before any late-payment penalty thresholds are met. For owner-managed businesses, that is money better kept in the business, and a clear reason to keep protecting cashflow front and centre of your attention.
Where we see businesses caught out
Most late-payment cases we deal with are not deliberate. They usually come from one of these patterns.
- VAT is treated as “money in the business” rather than a liability being held for HMRC.
- Tax set-asides are done informally, so they slip when trading gets busy.
- Forecasts focus on sales and overheads, but do not include tax peaks.
- Client or customer payment delays create a domino effect.
The UK Small Business Commissioner estimates that businesses are owed around £26bn in late payments at any given time. When that money is stuck in someone else’s bank account, HMRC still expects its share on time. Protecting cashflow is partly about dealing with customers, but it is also about making sure the tax elements of your pricing and billing never become accidental working capital.
Practical ways to stay ahead
Below are the approaches we recommend most often. None of them are complicated, but they work best when they’re part of a routine.
- Ring-fence tax early: Set up a separate bank pot and sweep a percentage of sales into it weekly. Even a rough rule, refined over time, supports protecting cashflow.
- Build tax into rolling forecasts: A 13-week cashflow forecast that includes VAT, PAYE and corporation tax dates shows pressure points before they hit. If you need help setting this up, our online bookkeeping support can keep your figures current enough to rely on.
- Keep VAT real-time: Late VAT is often a symptom of stale records. Up-to-date posting, clean bank feeds and regular reconciliations stop nasty surprises. We can review how you’re handling VAT and reporting so the numbers are stable quarter to quarter.
- Plan for seasonal spikes: Retailers, hospitality and project-based businesses often see uneven income. Map tax payments against your trading pattern, not against a flat average month.
- Use Time to Pay early: If cash is tight, don’t wait. HMRC will consider Time to Pay arrangements and interest will still run, but spreading the debt can prevent penalties and protect your wider cash position. We can talk you through what HMRC usually accepts and help you approach them with the right numbers.
The common thread is visibility. Protecting cashflow under this regime is less about finding extra money and more about avoiding blind spots.
What to do if you realise you’ll be late
If you spot a problem before the due date, you still have options. HMRC is far more receptive to early contact than to silence.
Our suggested order of action
- Review the true liability so you know the size of the gap.
- Check whether partial payment is possible. Paying something reduces daily interest straightaway.
- Contact HMRC quickly if you can’t clear it by the deadline, and ask for Time to Pay.
- Update your forecast so this does not become a repeated cycle.
Next steps for protecting cashflow
HMRC’s late-payment interest overhaul is here to stay, and the main takeaway is simple: lateness now costs more and it costs faster. With interest charged daily from day one for VAT, and the same base-rate-plus-4% rule applying across most taxes, short gaps can create a steady drip of avoidable cost. At the same time, the wider business environment is not making life easier – late payment remains widespread and billions of pounds are tied up in overdue invoices.
The good news is we can control most of the risk with better forward planning. Protecting cashflow is about treating tax as a scheduled outflow not a last-minute bill, keeping records current and using forecasts that show tax peaks as clearly as supplier and wage runs. If cash is likely to be tight, early action and a Time to Pay request can limit wider damage. Budget 2025 also signalled higher late-payment penalties from April 2027, so good habits around protecting cashflow and tax timing now should pay off even more over the next couple of years.
If you’d like us to review your upcoming VAT and tax timetable, sense-check your forecast, or help you set up a simpler system for protecting cashflow, book a chat with us. A short planning call now can save interest later, and it keeps your business in control rather than reacting under pressure.
