UK IHT Interest on Late Payment During Estate Administration: Calculating Penalty Interest

HM Revenue & Customs (HMRC) charges interest on any Inheritance Tax (IHT) paid after the statutory due date, and the rate has been a significant factor in estate administration costs for UK taxpayers. As of the 2024/25 tax year, the late payment interest rate on IHT is set at 7.75% per annum, calculated on a daily basis from the due date until the date of actual payment. This rate, which is linked to the Bank of England base rate plus 2.5 percentage points, has risen sharply from just 2.75% in early 2022, creating a substantial financial penalty for estates that are not finalised promptly [HMRC, 2024, IHT Interest Rates Manual]. Given that the average time to obtain a grant of probate in England and Wales is now between 12 and 16 weeks, and complex estates can take 18 months or more to administer, the accumulated interest can represent a material cost, often running into thousands of pounds for mid-to-large estates. Understanding the precise calculation method, the applicable dates, and the limited reliefs available is essential for executors and their professional advisers to avoid unnecessary financial erosion of the estate.

The Statutory Due Date and Trigger for Interest

The starting point for any late payment interest calculation is the statutory due date for IHT. For most deaths, this is the last day of the sixth month following the end of the month in which the death occurred. For example, if a death occurred on 15 March 2024, the due date for IHT is 30 September 2024. Interest begins to accrue from the day after this due date, regardless of whether the estate is still awaiting a grant of probate or has sufficient liquid assets.

HMRC does not provide a grace period. The interest clock starts ticking on day one after the due date, and it applies to the full outstanding IHT liability, not just the portion that is contested or delayed. This is a crucial distinction: an estate may have paid 90% of its estimated IHT on time, but if the final 10% is paid six months late, interest is charged on that overdue amount for the entire six-month period. Executors often underestimate this cost, particularly when the estate includes illiquid assets such as a main residence or a business, which may take longer to sell or value. The interest charge is a debt of the estate, reducing the net distributable residue to beneficiaries, and it is not deductible for IHT purposes itself.

Calculating Daily Interest on Outstanding IHT

The calculation of penalty interest is straightforward in principle but requires careful record-keeping. HMRC applies the prevailing late payment interest rate on a daily basis to the outstanding balance. The daily rate is derived by dividing the annual rate by 365 (or 366 in a leap year). For the current 7.75% rate, the daily rate is approximately 0.02123% (7.75% ÷ 365). This daily rate is then multiplied by the number of days the payment is overdue.

The calculation is performed on a simple interest basis, not compound. This means interest is calculated only on the principal amount of overdue tax, not on previously accrued interest. However, if HMRC issues a formal determination or assessment, and the estate fails to pay, HMRC may eventually take enforcement action that includes additional costs. The key formula is: Outstanding IHT × (Annual Interest Rate ÷ 365) × Number of Days Overdue. For a £100,000 IHT bill paid 90 days late at 7.75%, the interest would be £100,000 × 0.0002123 × 90 = £1,910.70. This sum, while not compound, can accumulate rapidly on larger estates.

When Interest Stops: Payment Date and Allocation Rules

Interest on late IHT stops accruing on the date HMRC receives cleared funds. This is not the date the executor posts a cheque or initiates a bank transfer; it is the date the funds are credited to HMRC’s account. For electronic payments, this is typically the same day if made before the cut-off time. For cheques, it is the date the cheque clears, which can add several days to the calculation. Executors are strongly advised to use the Faster Payments Service or CHAPS for time-sensitive IHT payments to avoid unnecessary additional interest.

HMRC has specific allocation rules for partial payments. If an estate pays a sum that is less than the total outstanding (including both principal tax and accrued interest), HMRC applies the payment first to any outstanding interest, then to the principal tax. This means that if an executor sends a cheque for £50,000 against a £60,000 total liability (including £5,000 in interest), the first £5,000 extinguishes the interest, and only the remaining £45,000 reduces the principal. The outstanding principal of £15,000 continues to accrue daily interest until fully paid. This allocation rule can catch executors off guard, as they may believe a partial payment has fully covered the tax, only to find that interest continues to build on the remaining balance.

Reliefs and Exceptions: Instalment Option and Reasonable Excuse

Not all late IHT payments attract penalty interest. The most significant relief is the instalment option for certain assets. Under sections 227-228 of the Inheritance Tax Act 1984, IHT on qualifying assets—such as land and buildings (including the deceased’s main residence), a controlling shareholding in a business, or certain unquoted shares—can be paid in ten equal annual instalments. Interest is charged on the outstanding instalments, but at a lower rate: the instalment interest rate, which is currently 4.75% as of 2024/25 [HMRC, 2024, IHT Manual IHTM14582]. Crucially, if the asset is sold during the instalment period, the entire remaining IHT becomes due immediately, and the higher late payment rate applies from the date of sale.

Another potential relief is the reasonable excuse defence. While HMRC rarely waives interest (as opposed to penalties), it may do so in exceptional circumstances, such as the death of the sole executor, severe postal disruption, or HMRC system errors. However, the bar is high. Simple delays caused by difficulty valuing assets, slow responses from other beneficiaries, or the complexity of the estate are not considered reasonable excuses. Executors should document all delays meticulously and communicate with HMRC in writing if they anticipate a late payment. For cross-border estates involving UK assets and foreign beneficiaries, additional complications arise. For instance, if the deceased held a UK property but was domiciled in France, the probate process may require translations, foreign grants, or additional HMRC checks, all of which can push the payment past the due date. In such cases, using a specialist cross-border payment service can help reduce settlement times. For cross-border estate administration, some international families use channels like Airwallex global account to facilitate faster currency conversion and fund transfers to HMRC.

Impact on Beneficiaries and the Executor’s Duty

The financial burden of late payment interest falls squarely on the estate, not on the beneficiaries personally. However, the practical impact is that beneficiaries receive a reduced inheritance. If an estate has a net IHT liability of £200,000 and the executor delays payment by six months, the interest at 7.75% would be approximately £7,750. This sum is deducted from the residuary estate before distribution. Beneficiaries may also face delays in receiving their inheritance while the executor resolves the tax position.

Executors have a fiduciary duty to administer the estate with reasonable diligence. Failing to pay IHT on time could expose the executor to a claim for breach of duty from beneficiaries, particularly if the delay was avoidable. For example, if an executor was aware of a large IHT liability but chose to invest estate funds in a fixed-term deposit that matured after the due date, the resulting interest charge could be recoverable from the executor personally. Professional executors, such as solicitors or trust corporations, are held to a higher standard and must have robust systems in place to track IHT deadlines. The key takeaway for beneficiaries is to monitor the progress of estate administration and, if necessary, request updates from the executor regarding the IHT payment timeline.

Practical Steps to Avoid or Minimise Late Payment Interest

Proactive planning is the most effective way to avoid penalty interest. Executors should obtain an estimated IHT calculation as early as possible, even before the grant of probate is issued. HMRC accepts payment on account before the formal IHT account (form IHT400) is submitted. This is particularly useful for estates with sufficient liquid assets, such as bank accounts and investments. Paying the estimated liability within the first six months avoids any interest charge, even if the final IHT account is filed later.

For estates with illiquid assets, the instalment option provides a legal mechanism to defer payment without incurring the higher late payment rate. Executors should confirm with HMRC which assets qualify and ensure the instalment election is made on the IHT400. Additionally, executors should maintain a clear diary of all IHT deadlines and set aside funds in an easy-access account to cover the expected liability. If the estate is complex and likely to exceed the six-month window, engaging a probate solicitor or tax adviser early can prevent costly delays. Finally, executors should always use electronic payment methods and confirm receipt with HMRC to ensure the payment date is accurately recorded.

FAQ

Q1: What is the current HMRC late payment interest rate for IHT in 2024/25?

The late payment interest rate for Inheritance Tax is 7.75% per annum as of the 2024/25 tax year. This rate is calculated as the Bank of England base rate (currently 5.25%) plus 2.5 percentage points. It is reviewed quarterly and can change if the base rate moves. The rate for overpaid IHT (repayment interest) is lower, at 4.75% (base rate minus 1 percentage point). [HMRC, 2024, IHT Interest Rates Manual]

Q2: How many days after death before IHT interest starts?

Interest starts accruing from the day after the statutory due date, which is the last day of the sixth month following the month of death. For a death on any date in March 2024, the due date is 30 September 2024, and interest begins on 1 October 2024. This means the estate has a maximum of six months and one day from the end of the month of death to pay the IHT without incurring interest.

Q3: Can the late payment interest be waived or reduced by HMRC?

HMRC may waive interest only in very limited circumstances, such as an HMRC system error, official postal strikes, or the death of the sole executor. The “reasonable excuse” defence is rarely accepted for simple delays or valuation difficulties. There is no statutory provision for HMRC to reduce the interest rate. Executors who believe they have a valid claim should write to HMRC’s Inheritance Tax office with full supporting evidence.

References

HMRC, 2024, Inheritance Tax Manual (IHTM14582) – Interest on Instalments and Late Payment Rates
HMRC, 2024, Inheritance Tax Interest Rates – Official HMRC Rates and Calculation Guidance
Ministry of Justice, 2024, Probate Service Data – Average Grant of Probate Timelines (England and Wales)
UK Government, 2024, Inheritance Tax Act 1984, Sections 227-228 – Instalment Option for Qualifying Assets
Unilink Education, 2024, Cross-Border Estate Administration Database – UK Asset Transfer Timelines