Understanding SDLT Charges on Substantial Performance and Completion of Contracts

SDLT when a land contract is substantially performed before completion

If a buyer effectively starts carrying out a land contract before the legal transfer is completed, SDLT can arise at that earlier stage. When the conveyance later completes, both the earlier contract and the later completion are still notifiable, but any SDLT due on completion is only the amount above the SDLT already chargeable on the substantially performed contract.

• Substantial performance usually means the buyer has taken a major step under the contract, such as taking possession or paying a substantial amount.
• SDLT may therefore become chargeable before the final transfer deed is executed.
• If the transaction is later completed by conveyance, that completion is a separate notifiable transaction.
• The later SDLT charge is reduced by the SDLT already chargeable on the earlier contract, so the same deal is not taxed twice in full.
• If the SDLT charge on completion is no higher than the earlier charge, there may be no extra SDLT to pay, even though the completion must still be reported.
• It is important to distinguish between whether a transaction is notifiable and whether any additional tax is actually payable.

Scroll down for the full analysis.

SDLT where a contract is substantially performed before completion

This page explains what happens for Stamp Duty Land Tax when a land contract is treated as having happened early because it has been substantially performed, and the legal transfer then takes place later. The key point is that there can be two notifiable transactions, but the tax is not simply charged twice on the same deal.

What this rule is about

SDLT is not always triggered only when the final transfer deed is completed. In some cases, a contract is treated as chargeable earlier if it has been substantially performed. Broadly, that means the buyer has already taken a significant step under the contract, such as taking possession or paying substantial consideration, so the tax system treats the contract as having enough practical effect to justify a charge at that stage.

If the parties later complete the transaction formally by conveyance, the law has to deal with the relationship between the earlier charge on the contract and the later completion transaction. The purpose of this rule is to prevent the same economic transaction from being taxed twice in full, while still recognising that the later conveyance is itself a separate notifiable event.

What the official source says

The HMRC manual says that if a contract has already been charged to SDLT because it was substantially performed, and that contract is later completed by a conveyance, both of the following are notifiable transactions:

• the contract that was substantially performed, and
• the transaction effected on completion by the conveyance.

However, the SDLT due on the later completion transaction is only the excess, if any, over the amount of SDLT already chargeable on the earlier contract.

In practical terms, the earlier substantial performance charge is taken into account when calculating what remains payable on completion.

What this means in practice

This rule matters where there is a gap between the contract becoming substantially performed and the final legal completion. That can happen, for example, where the buyer goes into possession before the transfer deed is executed.

The practical effect is:

• the earlier contract may need to be notified and taxed when substantial performance occurs;
• the later conveyance is still a notifiable transaction when completion happens; and
• the later SDLT charge is reduced by the SDLT already chargeable on the substantially performed contract.

So the later return is not ignored just because tax was already considered earlier. But equally, the legislation does not aim to impose a full second charge on the same deal if nothing relevant has changed.

If the tax chargeable on completion is no more than the tax already chargeable on the substantially performed contract, there may be no additional SDLT to pay on completion, even though the completion transaction is still notifiable.

How to analyse it

A sensible way to approach this issue is to ask the following questions in order:

• Was there a land contract that became substantially performed before formal completion?
• If yes, was that earlier contract already within the SDLT charge on that basis?
• Has the transaction now been completed by a conveyance?
• What SDLT is chargeable on the completion transaction?
• How much SDLT was chargeable on the earlier substantially performed contract?
• Is the tax on completion greater than the earlier amount? If so, only the excess is due on completion.

This comparison matters because the rule is about the amount of tax chargeable on each stage. The later completion transaction is not ignored. Instead, the earlier charge is effectively credited against the later one.

It is also important to keep separate the ideas of:

• notifiability, meaning whether a transaction must be reported, and
• tax payable, meaning whether any additional SDLT is actually due.

The source material makes clear that both transactions are notifiable. That does not necessarily mean tax is payable twice.

Example

Illustration: a buyer exchanges contracts to acquire land and is allowed into possession before legal completion. That early possession means the contract is substantially performed, so SDLT arises on the contract at that stage.

Some time later, the parties complete by executing the conveyance. The conveyance is a separate notifiable transaction. The buyer then works out the SDLT chargeable on completion and compares it with the SDLT already chargeable on the substantially performed contract.

If the amount chargeable on completion is the same as the amount already chargeable earlier, no further SDLT is due on completion. If the amount chargeable on completion is higher, only the difference is payable.

Why this can be difficult in practice

The short HMRC statement assumes that it is already clear whether substantial performance has happened. In real transactions, that can be the difficult part. Questions can arise about whether possession has genuinely been given, whether payments count in the relevant way, and exactly when the earlier charge arose.

There can also be practical complications if the figures relevant to the SDLT calculation are different by the time of completion. The source material does not spell out every possible reason why the later amount might be higher or lower, so the calculation must be done carefully by reference to the actual chargeable amount at each stage.

Another point that can cause confusion is the difference between tax that was chargeable and tax that was actually paid. The manual wording focuses on the amount of tax chargeable on the contract and on the later transaction. That legal comparison is the key mechanism described in the source.

Key takeaways

• If a land contract is substantially performed before legal completion, SDLT can arise before the conveyance is executed.
• When the deal is later completed by conveyance, both the earlier contract and the later completion transaction are notifiable.
• Any SDLT due on completion is only the excess over the SDLT already chargeable on the substantially performed contract.

This page was last updated on 24 March 2026

Useful article? You may find it helpful to read the original guidance here: Understanding SDLT Charges on Substantial Performance and Completion of Contracts

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