What happens if payment on account is late is a common concern for someone who has missed the 31 July instalment after a quieter period of work. HMRC may charge interest and late payment penalties, and the unpaid amount can remain due even if your income has fallen. This guide explains the likely consequences, what to do immediately, when reducing a payment on account may be appropriate, and how other Self Assessment charges can affect the total.
What happens if payment on account is late
A payment on account is an advance payment towards your next Self Assessment tax bill. It is usually split into two instalments, with the first normally due by 31 January and the second normally due by 31 July. Each instalment is generally based on an earlier tax liability, although the exact calculation can be affected by payments already made, tax deducted at source and the structure of your return.
If an instalment is not paid by its deadline, HMRC can charge late payment interest from the due date until the amount is cleared. The applicable interest rate can change, so you should check the current rate on GOV.UK rather than relying on an old calculation or an online example. Interest is separate from the tax itself and may continue to build while you are arranging payment.
Late payment penalties may also apply, depending on the tax year, the amount outstanding and how long the payment remains unpaid. The penalty timetable and rates are subject to legislation and can change, so confirm the current position with HMRC. A payment being only partly late does not necessarily remove the consequences: interest and any relevant penalty may apply to the balance that remains unpaid.
The first steps after missing the deadline
Start by checking your Self Assessment online account to establish which payment is overdue and whether HMRC has allocated a payment correctly. A bank transfer made close to the deadline can take time to appear, particularly around weekends and bank holidays, so retain proof of the payment date and reference used. If the account still shows a balance, do not assume that it will correct itself without checking with HMRC.
Paying as much as you can promptly will normally reduce the period during which interest can accrue, although it does not automatically cancel a penalty that has already become due. If you cannot clear the balance, contact HMRC to discuss a payment arrangement. HMRC will consider matters such as the amount owed, your income, expenditure and ability to maintain the proposed instalments, and an arrangement is not automatic.
A common mistake is to wait until the next Self Assessment deadline and pay both instalments together without checking the account. That can leave the earlier balance outstanding and create additional interest or penalties. Another mistake is using the wrong payment reference, which can delay allocation; check the payment instructions in your online account and keep confirmation of every transfer.
Can the payment on account be reduced
You may be able to reduce payments on account when you reasonably expect your current year liability to be lower than the amount used for the calculation. This can happen after a fall in trading profits, a period away from work, a large one-off income item in the previous year or a change in the tax you pay through employment. The reduction is made through your Self Assessment account, rather than by simply paying less than the amount requested.
Before reducing an instalment, prepare a realistic estimate of current-year income, allowable expenses, pension contributions and tax deducted at source. If the estimate is too optimistic, the eventual balancing payment can be larger than expected. HMRC may charge interest on an underpayment caused by an excessive reduction, and penalties could be relevant if the resulting liability is not paid on time.
Reduce only on reasonable grounds, not because the instalment is inconvenient. For example, imagine an illustrative taxpayer whose previous liability produced two requested instalments of £4,000 each, but whose current profits are expected to fall substantially. If a careful forecast suggests the total current liability is closer to £4,500, reducing the instalments could be sensible, but the taxpayer should retain the workings and plan for any balancing payment. These figures are purely illustrative and are not current tax thresholds or a prediction of an outcome.
Other Self Assessment amounts to check
A late payment on account may not be the only amount due. When you file the tax return, you may have a balancing payment for the previous tax year as well as the next year’s payments on account. Check the tax calculation rather than assuming that the overdue instalment is the full amount you need to budget for.
Different sources of income can change the calculation in ways that are easy to miss. For example, someone with employment income and freelance work may need to account for tax not collected through their PAYE code. The self assessment high income child benefit charge can also create an additional liability for an individual with adjusted net income above the relevant limit, so Child Benefit received by a household should be reviewed when estimating the bill.
Business owners sometimes focus on a late payment while overlooking claims that might correctly reduce taxable profit. Questions such as can directors claim home office expenses depend on the company arrangement, the work carried out and the records available; a director should not treat personal household costs as automatically deductible. Similarly, can incorporation relief apply to property partnerships is a specialist capital gains question, not a routine way to reduce a payment on account. Ask a qualified tax adviser: which figures belong in my current-year forecast, and which reliefs are actually available on my facts?
When to seek help with a late payment
Contact HMRC promptly if you believe the bill is wrong, a payment has not been allocated, or exceptional circumstances affected your ability to pay. HMRC may ask for supporting information, and any request to cancel or reduce a penalty is considered under the applicable rules rather than granted simply because the payment was difficult. Keep a clear record of dates, messages, payment confirmations and the explanation for the delay.
Professional help can be worthwhile where the account involves substantial arrears, several years of unfiled returns, foreign income, partnership income, property disposals or a dispute about an HMRC calculation. A qualified accountant or tax adviser can review the calculation and help communicate with HMRC, but they cannot guarantee that interest or penalties will be removed. Check the adviser’s qualifications, experience and terms before instructing them.
Time to Pay is not automatic, and agreeing an instalment plan does not necessarily erase interest or penalties. If you request one, ask what amount must be paid immediately, how the remaining balance will be collected, whether interest continues, and what happens if an instalment is missed. Confirm the arrangement in writing and make sure the proposed payments are affordable alongside the next tax deadline.
Key Takeaways
The practical answer to what happens if payment on account is late is that the overdue tax remains payable and HMRC may add interest and late payment penalties under the rules applying to that tax year. The longer the balance remains unpaid, the greater the potential cost can become. Paying promptly, or contacting HMRC when full payment is not possible, is generally more useful than ignoring the notice.
Check whether the amount is correct before changing it. If your income has genuinely fallen, a carefully supported reduction may be available, but an unjustified reduction can lead to a later balancing payment and interest. Include other possible liabilities, such as employment income not fully taxed through PAYE, the self assessment high income child benefit charge and income from property or a partnership.
Finally, verify current deadlines, interest rates, penalty rules and payment instructions on GOV.UK or with HMRC, because tax rules change between tax years. This publication is independent guidance, not HMRC, a regulated accountant or a tax adviser. For complex calculations, arrears, relief claims or disagreements with HMRC, seek advice from a suitably qualified professional.