Guide on Adjusting Land Transaction Tax for Contingency and Uncertainty Cases

SDLT changes when contingent or uncertain consideration is later settled

Where the price for land was not fully fixed when the transaction completed, SDLT may need to be corrected later. The key issue is whether the extra amount was contingent on a future event or simply uncertain and later became known, because that affects whether the buyer amends the original return, files a further return, or makes a repayment claim.

• For contingent consideration, the original SDLT return is made on the basis that the contingency will happen and the extra amount will be paid.
• If that contingency later fails permanently, the buyer may reduce the SDLT by amending the return within the normal time limit or, if that has passed, by making a repayment claim.
• For uncertain consideration, once the final amount is known, a further return may be required if extra SDLT is due or the transaction becomes notifiable or chargeable for the first time.
• Any recalculation uses the SDLT rates that applied on the effective date of the transaction, not the rates in force when the amount is later settled.
• HMRC says interest on underpaid SDLT in uncertainty cases runs from the effective date, while interest on overpaid tax generally runs from the date of payment.
• These cases can be difficult because contracts may mix contingency and uncertainty, and the correct route depends on whether the amendment window is still open.

Scroll down for the full analysis.

SDLT adjustments when contingent or uncertain consideration is later resolved

This page explains what happens for Stamp Duty Land Tax when the price for a land transaction was not fully fixed at the start. The rules differ depending on whether the extra amount depended on a contingency, or whether the amount was simply uncertain and later became known. That distinction matters because it affects when tax is paid, whether a further return is needed, and how any refund or extra tax is dealt with.

What this rule is about

Some land transactions do not have a final, fixed amount of consideration on the effective date. For example, part of the price may only become payable if something happens later, or the amount may be unknown at the time of completion.

The SDLT legislation contains special rules for these cases. The official material here focuses on what happens later, once the contingency falls away or the uncertain amount is finally known.

The key provisions mentioned are:

• FA 2003 section 51, which deals with contingent and uncertain consideration when the transaction is first reported
• FA 2003 section 80, which deals with later adjustments once the position becomes clear
• the amendment and repayment rules in Schedule 10 and Schedule 11A

In practical terms, the question is: after the original SDLT filing, has something happened that shows the original tax position was too high or too low?

What the official source says

HMRC draws a distinction between contingency cases and uncertainty cases.

In a contingency case, the original return is made on the assumption that the contingency will occur and that any additional consideration will become payable. If it later becomes clear that the contingency will never happen, the return must be adjusted under section 80.

If the time limit for amending the return is still open, the purchaser should amend the earlier return. If that amendment window has expired, the purchaser should make a repayment claim under Schedule 11A. If HMRC does not open an enquiry into the amendment, the SDLT is adjusted and any overpaid tax is repaid. HMRC says repayment interest runs from the date the tax was paid.

In an uncertainty case, or a mixed case involving both contingency and uncertainty, section 80 requires a land transaction return when the uncertain amount is finally ascertained if either:

• more SDLT becomes due, or
• the transaction becomes notifiable or chargeable for the first time

The return must include a self-assessment of the SDLT due on the basis of the newly known information. The tax is calculated using the rates in force at the effective date of the transaction, not the later date when the amount becomes known.

The manual also states that interest runs from the effective date of the transaction, not from the date the uncertainty is resolved.

Where the new information in an uncertainty case shows that too much tax was paid, the purchaser should seek a repayment by amending the return within the normal amendment window or, if that window has closed, by making a claim under Schedule 11A. HMRC says interest is payable on the overpaid tax from the date of payment.

The normal Schedule 10 framework also applies to returns made under section 80. That means HMRC can enquire into them, and late filing penalties can apply.

What this means in practice

The practical starting point is to identify what kind of variable consideration you had at the outset.

If the transaction involved a true contingency, the original SDLT filing assumes the contingency will happen. That usually means the buyer may have paid SDLT on an amount that never becomes payable. If the contingency later fails for good, the buyer may be entitled to have the SDLT reduced and obtain a refund.

If the transaction involved uncertainty, the issue is different. The amount was not yet known, and once it is known the SDLT position may need to be revisited. If the final figure means more tax is due, HMRC expects a further return and payment. If it means less tax is due, the buyer must actively claim the overpayment back.

Two practical points matter especially:

• the tax is recalculated by reference to the rates that applied on the effective date, so later rate changes do not alter the analysis
• interest on underpaid tax can run from the effective date, which means delay can become expensive even if the amount was only settled much later

The official material also distinguishes between cases where a transaction had already been notified and cases where it becomes notifiable for the first time once the uncertain amount is known. In the latter case, a formal land transaction return is required.

How to analyse it

A sensible way to approach these cases is to work through the following questions.

1. Was part of the consideration contingent, uncertain, or a mixture of both?

   This is the foundation of the analysis. A contingency means payment depends on whether an event happens. Uncertainty means the amount is not yet known. Some arrangements contain both features.

2. How was the original SDLT return completed?

   You need to know whether a return was filed, what assumptions were used, and whether SDLT was paid on an amount that was only expected or estimated.

3. What has now happened?

   Has it become clear that the contingency will never occur? Has the uncertain amount now been fixed? Does the new information increase the SDLT, reduce it, or make the transaction notifiable for the first time?

4. Is the normal amendment window still open?

   If yes, the route is usually to amend the return. If not, the route is generally a Schedule 11A claim for repayment where tax was overpaid.

5. Is a further return required?

   In uncertainty cases where more tax is due, or the transaction becomes notifiable or chargeable for the first time, HMRC says a return must be made within the relevant deadline once the amount is known.

6. What date is used for rates and interest?

   The rates are those in force at the effective date. For underpaid tax in uncertainty cases, HMRC says interest runs from that effective date.

Example

This is only an illustration of the mechanics.

A buyer acquires land for a fixed amount plus an extra payment if planning permission is granted within a stated period. On the original SDLT return, the legislation requires the filing to proceed on the assumption that the contingency will occur and the extra amount will become payable.

Two years later, the planning condition can no longer be satisfied and the extra payment will never be due. The buyer has therefore paid SDLT on too much consideration. If the normal amendment period has already expired, the buyer would need to use the repayment claim route referred to in the official material, rather than simply amending the original return.

By contrast, if the contract said that an additional amount would be payable but the exact figure depended on a later valuation exercise, that points more towards uncertainty. Once the figure is finally known, the SDLT position must be revisited. If the final number is higher than previously reflected, a further return and additional tax may be due, with interest running from the effective date.

Why this can be difficult in practice

The hardest issue is often classification. The official material assumes that you can identify whether the case involves contingency, uncertainty, or both. In real transactions, contractual pricing clauses are not always neatly drafted, and one clause may contain elements of each.

Another difficulty is timing. The route for correction depends on whether the amendment window is still open. Missing that deadline does not necessarily remove the right to a repayment, but it changes the mechanism and can affect how the claim needs to be presented.

There is also a practical difference between a transaction that was already notifiable and one that only becomes notifiable once the uncertain amount is known. The filing method is not the same in each case under the HMRC guidance.

Finally, the interest rule can catch buyers by surprise. In uncertainty cases where more SDLT becomes due, the manual says interest runs from the effective date rather than from the later date when the amount is finally ascertained. That can produce a significant interest charge even where the parties could not know the final amount at completion.

Key takeaways

• For contingent consideration, the original SDLT position assumes the contingency will happen; if it later becomes impossible, the buyer may need to amend the return or make a repayment claim.
• For uncertain consideration, once the amount is known a further SDLT return may be required if more tax is due or the transaction becomes notifiable for the first time.
• When SDLT is recalculated, the relevant rates are those at the effective date, and HMRC says interest on underpaid tax runs from that date as well.

This page was last updated on 24 March 2026

Useful article? You may find it helpful to read the original guidance here: Guide on Adjusting Land Transaction Tax for Contingency and Uncertainty Cases

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