Understanding SDLT Reliefs for Multiple Dwellings: Contract Variations and Tax Implications

SDLT and Multiple Dwellings Relief When Flat Numbers Change Before Completion

If a buyer pays for an unfinished residential block before legal completion, SDLT may already be due because the contract has been substantially performed. If the contract is later changed so the number of dwellings is reduced, HMRC says the SDLT position must be recalculated as if that change happened just before substantial performance, which can increase the tax due.

• HMRC’s example involves a contract to buy an unfinished block planned as six flats for £1.2 million, with the full price paid before completion.
• Because full payment counts as substantial performance, SDLT is triggered before completion and multiple dwellings relief is worked out by reference to the dwellings in the original contract.
• If the contract is later varied so there are fewer dwellings, such as four flats instead of six for the same price, HMRC says the SDLT must be recalculated using the lower number.
• This usually increases SDLT because the same price is spread across fewer dwellings, and the buyer must file a further SDLT return within 30 days of the variation and pay the extra tax.
• The higher rates for additional dwellings may apply, and non-resident rates may also apply where relevant.
• If the number of dwellings increases after substantial performance, HMRC’s stated view is that the increase is ignored for SDLT purposes.

Scroll down for the full analysis.

Multiple dwellings relief where the number of flats changes before completion

This page explains how SDLT can change if a buyer agrees to buy an uncompleted residential block, pays before completion, and the contract is later changed so that the number of dwellings is reduced. The point matters because SDLT may already have been triggered by substantial performance, and a later contract variation can change the tax position.

What this rule is about

The source deals with multiple dwellings relief in a particular situation: a buyer contracts to acquire more than one dwelling, the contract is substantially performed before legal completion, and the development plans are then changed.

In SDLT, substantial performance can bring the transaction into charge before completion. Where the purchase involves multiple dwellings, the SDLT calculation may depend on the number of dwellings being acquired. If that number later changes because the contract is varied, the tax result may also change.

The example in the HMRC manual focuses on a reduction in the number of dwellings. It also makes the separate point that the higher rates for additional dwellings may apply, and that the non-resident rates may also apply if relevant.

What the official source says

HMRC’s example starts with a contract to buy the freehold of an uncompleted block of six flats for £1.2 million. The buyer pays the full price before completion. Six months later, the contract is varied so that instead of six flats, the building will contain four larger flats. The total price stays the same.

HMRC treats the original purchase as a relevant transaction involving more than one dwelling, namely the six flats. Because the full consideration was paid, the contract was substantially performed at that point. SDLT was therefore triggered then.

HMRC says the tax rate was initially determined by dividing the total consideration by the number of dwellings. On those facts, the higher rates for additional dwellings apply, and the non-resident rates may also apply if any buyer is non-UK resident.

When the contract is later varied to reduce the number of flats from six to four, HMRC says that variation is treated as having happened immediately before substantial performance. The SDLT must therefore be recalculated by dividing the same consideration by the revised number of dwellings.

Because reducing the number of dwellings increases the amount attributable to each dwelling, the SDLT increases. HMRC says the buyer must file a further return within 30 days of the variation and pay the extra tax.

The example also states the opposite result if the number of flats had increased. In that case, HMRC says the change would be ignored for SDLT purposes.

What this means in practice

The practical effect is that SDLT does not necessarily stay fixed just because it was triggered earlier by substantial performance. If the contract is later changed in a way that reduces the number of dwellings, HMRC’s view is that the variation is read back to the time immediately before substantial performance. That can produce a higher SDLT bill.

This matters particularly for off-plan and development transactions. A buyer may think they acquired six dwellings for SDLT purposes because that was the original design. But if the parties later agree to build four larger dwellings for the same price, HMRC’s approach is to recalculate the tax by reference to four dwellings, not six.

That can affect:

• whether multiple dwellings relief gives as much benefit as first expected
• the amount of SDLT due under the rate-setting calculation
• the need to submit a further SDLT return after the variation
• cash flow, because extra tax may become payable after the original filing

The example also shows that not every later change helps the buyer. If the number of dwellings goes up after substantial performance, HMRC says that increase is ignored. So a buyer cannot assume that a redesign increasing the number of units will improve the SDLT position retrospectively.

How to analyse it

A sensible way to analyse this type of case is to work through the following questions.

• What was being acquired under the original contract? Identify how many dwellings the contract covered at the time it was first made.
• Was there substantial performance before completion? Full payment of the consideration is one example given in the source.
• Was the transaction one involving multiple dwellings? If so, the SDLT calculation may depend on the number of dwellings.
• Was the contract later varied? If yes, what exactly changed: the number of dwellings, the layout, the consideration, or something else?
• Did the variation reduce the number of dwellings? On HMRC’s example, a reduction is treated as occurring immediately before substantial performance, so SDLT is recalculated on that basis.
• Did the variation increase the number of dwellings instead? HMRC’s example says that increase is ignored for SDLT purposes.
• Do the higher rates for additional dwellings apply? The manual says they do on the facts of the example.
• Do the non-resident rates apply? The manual says they may apply if any purchaser is not UK resident.
• Has the variation increased the SDLT due? If so, HMRC says a further return must be filed within 30 days of the variation and the extra tax paid.

The key practical point is to compare the SDLT position at substantial performance with the SDLT position after applying HMRC’s treatment of the later variation.

Example

Illustration: A company agrees to buy the freehold of an unfinished residential block for £1.2 million. The contract provides for six flats. The company pays the full price before legal completion, so the contract is substantially performed and SDLT is calculated at that stage by reference to six dwellings.

Later, the parties agree to redesign the scheme so that there will be four larger flats instead, for the same £1.2 million. Under HMRC’s approach in this example, the variation is treated as if it happened immediately before substantial performance. The SDLT must therefore be recalculated by reference to four dwellings, not six. Because the same price is now spread across fewer dwellings, the SDLT increases. A further return is needed within 30 days of the variation, together with payment of the extra SDLT.

Why this can be difficult in practice

The difficult part is often identifying exactly what the buyer contracted to acquire, and whether a later change is truly a variation of that contract rather than a separate arrangement or a change in how the development is implemented.

It can also be easy to miss the compliance consequence. If SDLT was already reported when the contract was substantially performed, the parties may not revisit the SDLT position when the plans later change. HMRC’s example shows that they should.

Another practical difficulty is that the source gives a clear result where the number of dwellings falls, but only a brief statement where the number rises. The manual says an increase would be ignored for SDLT purposes, but the source does not explore the boundaries of that proposition. In real cases, the precise drafting of the contract variation and the wider facts may matter.

The interaction with the higher rates and non-resident rates can also complicate the calculation. The source flags that those rates may apply, but does not set out the detailed rules for them on this page.

Key takeaways

• If a contract for multiple dwellings is substantially performed before completion, SDLT can arise at that stage.
• If the contract is later varied so the number of dwellings is reduced, HMRC’s view is that the variation is treated as happening immediately before substantial performance and the SDLT may increase.
• Where extra SDLT becomes due because of the variation, HMRC says a further return must be filed within 30 days and the additional tax paid.

This page was last updated on 24 March 2026

Useful article? You may find it helpful to read the original guidance here: Understanding SDLT Reliefs for Multiple Dwellings: Contract Variations and Tax Implications

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