Land Transaction Tax when the final price is uncertain
Uncertain property prices and LTT
If part of the price depends on a future event, you normally estimate it reasonably at completion for Land Transaction Tax.
- Use evidence available at completion
- Keep the estimate under review
- Consider whether a qualifying deferral is available
Scroll down for the full analysis.
Read the original guidance here:
Land Transaction Tax when the final price is uncertain
If part of your property price depends on what happens later, you still need to deal with Land Transaction Tax now. You usually make a reasonable estimate at completion. Land Transaction Tax replaced stamp duty land tax in Wales in 2018.
What this rule is about
Sometimes the final price cannot be known on completion. For example, an extra payment may depend on future sales, planning, profits or another future event.
Lawmakers call this uncertain consideration in legislation. Part of your payment remains uncertain.
That distinction matters. You calculate LTT when the transaction takes effect, normally on completion, even when later payments depend on conditions that have not happened and whose amounts remain unknown. Completion sets the point.
What the official source says
WRA says you must make a reasonable estimate of the final amount at the effective date. The legislation requires the same approach when the amount or value is uncertain or not yet known.
- The uncertainty must arise because of future events.
- You should estimate the amount reasonably at completion.
- The estimate should cover the final amount you expect to pay.
- If the future event seems unlikely, WRA says it may be reasonable to request a nil deferral.
What this means in practice
You cannot simply leave an uncertain payment out of your LTT calculation when it may never be due, because you must use a reasonable figure based on what was known at completion. Include it now.
If the payment later becomes fixed, the tax position may change. More tax can mean a further return. Less tax can allow you to amend the return or seek repayment.
- Keep the facts and figures used for your estimate.
- Check whether a later payment could alter the LTT due.
- Record the date when the final amount becomes known.
- Do not assume a deferral removes the tax permanently.
How to analyse it
Start with the contract. The key question is simple: is the extra payment unknown because of a future event, or is it already capable of being worked out?
- Identify every part of the price payable after completion.
- Read the condition that triggers, changes or ends that payment.
- Decide what information was available at completion.
- Make and record a reasonable estimate using that information.
- Check whether any qualifying tax may be deferred.
- Monitor the event until the amount becomes known.
Example
Amir buys land for £300,000. He may also pay up to £50,000 if a future event happens. At completion, the available evidence supports an estimate of £20,000. His LTT calculation should use £320,000, not just the £300,000 paid straight away. If the final extra payment is later fixed at £35,000, he should check whether a further return and more tax are due.
Why this can be difficult in practice
Spotting later payments is easy. The difficult part is deciding what a reasonable estimate was on the day of completion. Later events do not, by themselves, prove that the earlier estimate was unreasonable.
WRA’s guidance mentions a nil deferral where the future event is unlikely. That is not a promise that WRA will agree. The statutory conditions for a deferral still apply.
- A hoped-for outcome is not evidence for an estimate.
- A maximum possible payment is not always the reasonable estimate.
- Deferral requests need to be made with the first return and meet specific conditions.
- Interest on deferred amounts is covered by separate WRA guidance.
Key takeaways
- Estimate an uncertain future payment reasonably at completion.
- Keep evidence showing how you reached that figure.
- Check the position again when the final amount becomes known.
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
- LTTA 2017 section 18 — what counts as the amount paid for land
- LTTA 2017 section 20 — estimating uncertain or unascertained amounts paid
- LTTA 2017 section 47 — further returns when an uncertain amount becomes known
- LTTA 2017 section 48 — repayment where the final tax is lower
- LTTA 2017 section 58 — requests to defer tax on uncertain amounts
- LTTA 2017 section 59 — working out the maximum tax that can be deferred
- LTTA 2017 section 61 — when deferred tax must be paid
- LTTA 2017 section 71 — the date that normally counts as completion
Official guidance
The pages below are the Welsh Revenue Authority’s guidance. Guidance is not law. It sets out how the Welsh Revenue Authority 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. the Welsh Revenue Authority can also change or withdraw guidance, and it may not cover your facts.
- Welsh Revenue Authority, Chargeable consideration technical guidance: Uncertain consideration
- Welsh Revenue Authority, Land Transaction Tax returns and payments technical guidance: interest on deferred amounts
Where this is not settled
- What is a reasonable estimate depends on the contract, the future event and the evidence available at completion.
- The source says a nil deferral request may be reasonable where the future event is unlikely, but it does not give examples or a detailed test.
- The supplied statutory material has no identifiable currency notice or date, so the current procedural position should be checked before relying on it.
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 that could change the price
- Details of the future event on which payment depends
- Forecasts, valuations and calculations supporting the estimate
- Evidence of when the final amount becomes known
- Any deferral request and WRA decision notice
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 Land Transaction Tax (LTT), the tax on property in Wales. It replaced Stamp Duty Land Tax in Wales on 1 April 2018, and SDLT does not apply in Wales. MY QUESTION Land Transaction Tax when the final price is uncertain [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 - LTTA 2017 section 18 - what counts as the amount paid for land https://www.legislation.gov.uk/anaw/2017/1/section/18 - LTTA 2017 section 20 - estimating uncertain or unascertained amounts paid https://www.legislation.gov.uk/anaw/2017/1/section/20 - LTTA 2017 section 47 - further returns when an uncertain amount becomes known https://www.legislation.gov.uk/anaw/2017/1/section/47 - LTTA 2017 section 48 - repayment where the final tax is lower https://www.legislation.gov.uk/anaw/2017/1/section/48 - LTTA 2017 section 58 - requests to defer tax on uncertain amounts https://www.legislation.gov.uk/anaw/2017/1/section/58 - LTTA 2017 section 59 - working out the maximum tax that can be deferred https://www.legislation.gov.uk/anaw/2017/1/section/59 - LTTA 2017 section 61 - when deferred tax must be paid https://www.legislation.gov.uk/anaw/2017/1/section/61 - LTTA 2017 section 71 - the date that normally counts as completion https://www.legislation.gov.uk/anaw/2017/1/section/71 Guidance page from the Welsh Revenue Authority on this topic (guidance, not law): https://www.gov.wales/chargeable-consideration-technical-guidance HOW I WANT YOU TO ANSWER 1. Work from the legislation above. Read it before answering. Guidance from the Welsh Revenue Authority is its 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 - What is a reasonable estimate depends on the contract, the future event and the evidence available at completion. - The source says a nil deferral request may be reasonable where the future event is unlikely, but it does not give examples or a detailed test. - The supplied statutory material has no identifiable currency notice or date, so the current procedural position should be checked before relying on it. Do not give me a conclusion you cannot support from the provisions above.
Legislation links show the Land Transaction Tax and Anti-avoidance of Devolved Taxes (Wales) Act 2017 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 4 September 2026
Useful article? You may find it helpful to read the original guidance here: Land Transaction Tax when the final price is uncertain
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