Stamp duty when a later payment changes or becomes certain
When a later payment changes stamp duty
A property price can include a sum that depends on a future event or cannot yet be measured exactly. SDLT is dealt with at the start, then reconsidered when the facts become clear.
- Use the original effective-date rules for the revised calculation.
- More SDLT can trigger a short filing deadline.
- Less SDLT may lead to an amendment or repayment claim.
Scroll down for the full analysis.
Read the original guidance here:
Stamp duty when a later payment changes or becomes certain
If part of your property price depends on what happens later, your stamp duty bill may need to change too. You may pay more or recover SDLT.
What this rule is about
Some property deals have a price that is not fixed on completion day. You may agree an extra payment if an authority grants planning permission, a business reaches a target, or another future event happens. The price can therefore remain open.
There are two main types. A contingent payment depends on whether an event happens. An uncertain payment will be made, but nobody yet knows its final amount.
For SDLT, the starting point can feel unfair: the law does not wait for the future. It uses an assumption or a reasonable estimate when you make the original return.
Later, the facts may prove that assumption wrong. Section 80 of the Finance Act 2003 lets you revisit the SDLT position.
What the official source says
HMRC’s manual explains the procedure when a later event changes the amount you pay for the property, although the manual is HMRC guidance rather than the law itself. The legal rules are in sections 51 and 80.
For a contingent payment, the original SDLT calculation assumes that the payment will become due. If a payment would stop on an event, the calculation assumes it will not stop.
- If later facts show that the event will not happen, you may need to revise the SDLT result because the original calculation assumed that the payment would become due. Act on the new facts.
- If the later facts mean less SDLT is due, and you remain within the allowed amendment period, you can amend the return to reflect those facts. Do not delay.
- After that period, section 80 allows a claim for repayment instead, subject to the statutory claim rules.
- If the amount was uncertain, the first return uses a reasonable estimate of the amount you will pay.
- Once you know the final amount, you must file a further return if more SDLT is due.
- You must also file a return if the transaction becomes notifiable for the first time.
The reason for the further return sets the time limit. If the transaction becomes notifiable for the first time, you must make it within 14 days. In other cases where SDLT, or extra SDLT, becomes due, the deadline is 30 days.
The later return must include a fresh calculation based on the information then known. You work out the tax using the rules and rates that applied on the transaction’s effective date. You do not use later rates.
What this means in practice
The key question is not simply whether money changes hands later. Ask why it changes. Was the extra amount dependent on an event, or was it always due but impossible to price exactly at the start?
That distinction decides how you should have made the first SDLT calculation and what should happen next.
- Keep the contract clause that explains the later payment.
- Keep proof of the later event, such as a planning decision or a final accounts statement.
- Compare the original SDLT calculation with the calculation using the final facts.
- Check whether the result means more SDLT, less SDLT, or a newly notifiable transaction.
- Record the date when the amount became known or the event was settled.
- Do not use today’s SDLT rates for the revised calculation.
More tax can be costly even if the final amount was impossible to know at completion. Interest on unpaid SDLT generally runs from the original effective date, where payment was not deferred. It does not wait until the amount becomes certain.
For a repayment, HMRC’s manual says interest is due from the date you paid too much tax. That is HMRC’s stated view in this guidance.
How to analyse it
Start with the paperwork, not the label used in emails. Calling a payment a bonus, uplift or deferred sum does not settle its SDLT treatment.
- Find the exact wording that says when the later amount is payable or stops being payable.
- Decide whether the payment was contingent, uncertain, or partly both.
- Check what was included in the original SDLT return and why.
- Identify the later event and the date when its outcome became clear.
- Recalculate SDLT using the effective-date rules and the final information.
- If more SDLT is due, check whether the 14-day or 30-day route applies.
- If less is due, check whether the return can still be amended.
- If not, consider a standalone repayment claim and retain proof that the SDLT was paid.
Section 80 uses HMRC’s return system. HMRC can enquire into a later return under section 80. HMRC can also check an amendment or repayment claim.
Example
Priya buys land for £400,000. Her contract says she will pay a further £50,000 if planning permission is granted. When Priya files the original return, she calculates SDLT using £450,000 because the extra sum depends on a future event and the calculation assumes it will become due. That assumption applies at the start.
Two years later, planning permission is finally refused and there is no further appeal. It is now clear that the £50,000 will never be paid. Priya should reconsider the SDLT result using £400,000 rather than £450,000.
If Priya is still within the period for amending the return, she can amend it. If not, section 80 allows a repayment claim. The contract, planning decision and evidence of the original SDLT payment will matter.
Change one fact and the answer changes. If permission is granted and the £50,000 becomes payable, there is normally no reduction based on that contingency. The original calculation already assumed the extra sum would be paid.
Why this can be difficult in practice
People often focus on the date they make the later payment. That is not always the key date. What matters may be when the amount became known, or when it became clear that the event would or would not happen.
Mixed clauses are particularly awkward. A contract can make part of a payment depend on an event while requiring the parties to calculate its size later, so the clause may combine a contingency with an uncertain amount. Both features matter.
- A payment described as deferred is not automatically contingent.
- A final accounts process may fix an uncertain amount rather than create a new payment.
- The original return may have used an estimate that needs checking against the contract.
- Interest can run from much earlier than the date of the final calculation.
- HMRC’s manual refers to an SDLT1, a letter in some cases and a Birmingham office address, but those administrative instructions should be checked before use.
There are also limits to this rule. Section 80 does not apply to the extent that the amount consists of rent. It also contains special limits on some lease-related repayment claims.
Key takeaways
- SDLT can change when a later payment becomes certain or falls away.
- More SDLT may require a return within 14 or 30 days.
- Less SDLT may be recovered by amendment or a repayment claim.
Technical analysis
For advisers, and for anyone who wants to check the law behind this page. You do not need this section to understand the guidance above.
Legislation
- FA 2003 section 51 — how contingent and uncertain prices are treated initially
- FA 2003 section 80 — later adjustments when a price becomes known
- FA 2003 section 87 — interest on extra tax from the original date
- FA 2003 Schedule 10 para 6 — time limit for amending a land transaction return
- FA 2003 Schedule 10 para 12 — HMRC enquiries into returns and later amendments
- FA 2003 Schedule 11A para 1 — standalone repayment claims and supporting records
- FA 2003 Schedule 11A para 6 — giving effect to claims and HMRC claim enquiries
Official guidance
The pages below are HMRC’s guidance. Guidance is not law. It sets out how HMRC reads the legislation, and it is not binding on you, on a tribunal or on a court. Where guidance and the legislation differ, the legislation wins. HMRC can also change or withdraw guidance, and it may not cover your facts.
Where this is not settled
- The source does not give an overall time limit for a standalone section 80 repayment claim after the amendment period ends.
- The current HMRC filing method and postal address should be checked before sending a later return or claim.
- The supplied legislation is current only to 17 November 2025. Current law must be checked for events after that date.
Evidence you would need
This kind of case is decided on the facts of the individual property. These are the records that usually settle it, and the ones an adviser would ask you for.
- The contract and any clause dealing with the later payment
- Proof of the event that fixed the amount or showed it would not happen
- The original SDLT return and payment records
- Calculations showing the original and revised amounts
- Dates for completion, the later event and any earlier return
Explore this with an AI
Readers often want to test their own situation. Copy the prompt below into ChatGPT, Claude or Gemini. It hands the model the actual legislation for this page rather than letting it answer from memory, and tells it to be explicit about what is uncertain. What comes back is information, not advice – check it against the links above.
I am researching UK Stamp Duty Land Tax (SDLT), which applies in England and Northern Ireland. MY QUESTION Stamp duty when a later payment changes or becomes certain [Replace this with your own situation: what you are buying, the price, the dates, who the buyer is, and what you plan to do with the property.] THE LAW THIS TURNS ON - FA 2003 section 51 - how contingent and uncertain prices are treated initially https://www.legislation.gov.uk/ukpga/2003/14/section/51/2025-11-17 - FA 2003 section 80 - later adjustments when a price becomes known https://www.legislation.gov.uk/ukpga/2003/14/section/80/2025-11-17 - FA 2003 section 87 - interest on extra tax from the original date https://www.legislation.gov.uk/ukpga/2003/14/section/87/2025-11-17 - FA 2003 Schedule 10 para 6 - time limit for amending a land transaction return https://www.legislation.gov.uk/ukpga/2003/14/schedule/10/paragraph/6/2025-11-17 - FA 2003 Schedule 10 para 12 - HMRC enquiries into returns and later amendments https://www.legislation.gov.uk/ukpga/2003/14/schedule/10/paragraph/12/2025-11-17 - FA 2003 Schedule 11A para 1 - standalone repayment claims and supporting records https://www.legislation.gov.uk/ukpga/2003/14/schedule/11A/paragraph/1/2025-11-17 - FA 2003 Schedule 11A para 6 - giving effect to claims and HMRC claim enquiries https://www.legislation.gov.uk/ukpga/2003/14/schedule/11A/paragraph/6/2025-11-17 HMRC's guidance page on this topic (guidance, not law): https://www.gov.uk/hmrc-internal-manuals/stamp-duty-land-tax-manual/sdltm50300 HOW I WANT YOU TO ANSWER 1. Work from the legislation above. Read it before answering. HMRC guidance is HMRC's view of the law, not the law, and does not bind a tribunal or a court. 2. Tell me what the rule actually requires, in plain English. 3. Tell me which facts decide the answer, and which facts would change it. 4. Tell me what evidence I would need to support the position. 5. Be explicit about anything unsettled or fact-sensitive. Do not guess. 6. Your training data has a cutoff and SDLT rates and reliefs change at fiscal events. Say so if you are not sure the law is current. POINTS ALREADY KNOWN TO BE UNCERTAIN ON THIS TOPIC - The source does not give an overall time limit for a standalone section 80 repayment claim after the amendment period ends. - The current HMRC filing method and postal address should be checked before sending a later return or claim. - The supplied legislation is current only to 17 November 2025. Current law must be checked for events after that date. Do not give me a conclusion you cannot support from the provisions above.
Legislation links show Finance Act 2003 as it stood on 2025-11-17. The law may have changed since, and the rules that apply are those in force on the date of your transaction. The official guidance this page is based on is here.
This page was last updated on 1 September 2026
Useful article? You may find it helpful to read the original guidance here: Stamp duty when a later payment changes or becomes certain
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