Interest on Unpaid Tax: Relevant Dates and Exceptions Explained

When interest starts on unpaid SDLT

Interest on unpaid Stamp Duty Land Tax usually starts after the payment deadline measured from the transaction’s effective date, but not always. If certain SDLT reliefs are later withdrawn, or HMRC has agreed to defer payment, the interest start date is based on the later disqualifying event or the deferred due date instead of the original transaction date.

• In most cases, interest runs from the end of the SDLT filing and payment period counted from the transaction’s effective date.
• For older cases, HMRC refers to interest starting 30 days after the relevant date; from 1 March 2019, this is generally 14 days where the return and tax are due within 14 days.
• If group relief, reconstruction relief, acquisition relief, or charities relief is later withdrawn, the relevant date is the date the disqualifying event happens.
• If HMRC has formally agreed deferred payment under section 90 of Finance Act 2003, interest starts from the date the deferred amount becomes due.
• The key practical step is to identify the correct SDLT liability, find the right relevant date, and then apply the correct 30-day or 14-day deadline.
• A common mistake is to assume interest always runs from the original completion date, when the legislation may instead point to a later date.

Scroll down for the full analysis.

When SDLT interest starts running on unpaid tax

This page explains the date from which interest is charged if Stamp Duty Land Tax (SDLT) is not paid on time. The key point is that interest does not always run from the transaction date itself. In most cases it is linked to the transaction’s effective date, but there are important exceptions, especially where a relief is later withdrawn or payment has been formally deferred.

What this rule is about

SDLT is not just about how much tax is due. It also matters when the tax must be paid. If tax remains unpaid after the permitted period, interest can be charged.

The legal issue here is the “relevant date”. That date is important because the interest clock runs by reference to it. To work out whether interest is due, and from when, you first need to identify the correct relevant date for the particular SDLT liability.

What the official source says

The HMRC manual says that interest is payable on unpaid SDLT under section 87 of Finance Act 2003.

It states that:

• for most cases, interest is payable from 30 days after the relevant date;
• from 1 March 2019, where a return and tax are required within 14 days, interest is payable from 14 days after the relevant date.

For most transactions, the relevant date is the effective date of the transaction.

The manual then identifies specific exceptions:

• if group relief is withdrawn, the relevant date is the date the disqualifying event occurs;
• if reconstruction relief or acquisition relief is withdrawn, the relevant date is the date the disqualifying event occurs;
• if charities relief is withdrawn, the relevant date is the date the disqualifying event occurs;
• if HMRC has agreed a deferred payment under section 90 of Finance Act 2003, the relevant date is the date the deferred amount falls due.

What this means in practice

In an ordinary SDLT case, the starting point is simple. Identify the transaction’s effective date. Then ask what filing and payment window applied at the time. If the tax was not paid by the end of that period, interest starts running immediately after it.

For older cases, the manual refers to a 30-day period after the relevant date. For cases where the SDLT return and payment were required within 14 days, interest starts 14 days after the relevant date.

The practical importance of the exceptions is that they move the interest start date away from the original transaction date.

That matters most where relief was originally claimed correctly, but later lost because of a later event. In that situation, the tax may only become chargeable because a disqualifying event happens afterwards. The manual indicates that interest then runs by reference to the date of that later event, not the original acquisition date.

Similarly, where payment has been formally deferred under the legislation and HMRC has agreed that deferral, interest runs from the date the deferred amount becomes due, not from the original transaction date.

How to analyse it

A sensible way to approach this issue is:

• Identify the SDLT liability in question. Is it the original tax on the transaction, tax arising because relief has been withdrawn, or a deferred amount becoming due?
• Find the correct relevant date. In most cases this is the effective date of the transaction, but for the specific relief-withdrawal and deferral cases listed above it is a different date.
• Check which filing and payment deadline applied at the time. The manual distinguishes between the older 30-day rule and the 14-day rule applying from 1 March 2019 where a return and tax are required within 14 days.
• Count forward from the relevant date by the applicable period.
• If tax remained unpaid after that point, interest is payable from then onwards.

Questions worth asking include:

• Was the tax due from the outset, or did it arise only because a relief was later withdrawn?
• If relief was withdrawn, exactly when did the disqualifying event occur?
• Was there a valid and agreed deferred payment arrangement under section 90?
• Does the transaction fall into the period where the 14-day filing and payment timetable applied?

Example

Illustration: a company acquires property and claims group relief. At the time of the transaction, no SDLT is payable because the relief applies. Later, a disqualifying event occurs so that the relief is withdrawn. On the approach set out in the HMRC manual, the relevant date for interest is the date of that disqualifying event. Interest does not run by reference to the original acquisition date in this type of case.

Why this can be difficult in practice

The main difficulty is that people often assume interest always runs from the original completion date. The manual shows that this is not always right.

Another difficulty is identifying the exact date of a disqualifying event. In relief-withdrawal cases, that date can be crucial, because even a small error may affect the interest calculation.

It is also important not to confuse the legislation with the manual. The manual explains HMRC’s view of how section 87 and the relevant relief provisions operate, but the legal answer ultimately depends on the legislation itself.

Finally, timing rules have changed over time. The manual refers both to a 30-day period and, from 1 March 2019 where applicable, a 14-day period. So the correct interest start date depends not only on the type of liability, but also on the timing regime that applied to that transaction.

Key takeaways

• In most SDLT cases, interest on unpaid tax runs from the end of the filing and payment period measured from the transaction’s effective date.
• Where certain reliefs are later withdrawn, the relevant date is the date of the disqualifying event, not the original transaction date.
• Where payment has been validly deferred, the relevant date for interest is the date the deferred amount falls due.

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Useful article? You may find it helpful to read the original guidance here: Interest on Unpaid Tax: Relevant Dates and Exceptions Explained

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