Do you pay SDLT when adding your spouse to a buy-to-let mortgage?

Introduction

People often ask whether Stamp Duty Land Tax (SDLT) is due when one spouse adds the other to a property that is already owned in one name. The question usually comes up where the property is being kept as a buy-to-let, the couple already own another home together, and the transfer is being done for income tax planning rather than for a sale price.

The key point is that SDLT is not based only on cash changing hands. If the incoming spouse takes on responsibility for part of an existing mortgage, HMRC can treat that assumed debt as chargeable consideration. Whether any SDLT is actually payable then depends on how much debt is being taken on and whether the higher rates for additional dwellings apply.

The Question

A homeowner bought a property in sole name some years ago and originally lived in it as a home. Later, the couple bought another property together and moved into that new home. The first property is now to be retained as a buy-to-let.

The homeowner wants to add their spouse to the first property and its mortgage so that rental income can be shared more efficiently for tax purposes. The property is worth about £200,000 and has an outstanding mortgage of about £33,000. No cash is being paid between spouses. The transfer is expected to complete on or after 2 April 2025.

The practical questions are:

• Will SDLT arise when the spouse is added?
• If so, how much?
• Does the answer change because the couple already own another home together?

Nick’s Explanation

Nick’s core point was that the SDLT analysis turns on consideration, and mortgage debt can count as consideration even if no money is paid between the spouses.

In anonymised form, his explanation was:

• If equity is simply gifted and the incoming spouse does not take on mortgage debt, there may be no SDLT consideration.
• If the incoming spouse takes on part of the mortgage, that assumed debt is treated as consideration for SDLT purposes.
• Because spouses are looked at together for additional dwelling purposes, the higher residential rates may apply to the chargeable consideration.
• However, if the amount of mortgage debt assumed is less than £40,000, no SDLT is payable on the transfer.

That last point was decisive on these facts, because the total mortgage balance mentioned was below £40,000.

The Law

SDLT is charged under the Finance Act 2003 on land transactions where there is chargeable consideration.

The main provisions relevant here are:

• Finance Act 2003, section 43: transactions between connected persons can still be chargeable.
• Finance Act 2003, Schedule 3, paragraph 1: no SDLT is charged where there is no chargeable consideration.
• Finance Act 2003, Schedule 4, paragraph 8: where property is transferred subject to an existing debt, or the transferee assumes liability for debt such as a mortgage, that debt can count as chargeable consideration.
• Finance Act 2003, Schedule 4ZA: higher rates for additional dwellings may apply to purchases of major interests in dwellings.

There is also an important threshold rule in the higher rates legislation. A transaction is not a “higher rates transaction” if the chargeable consideration is less than £40,000. In practice, that means that where the only consideration is assumed mortgage debt below £40,000, the higher rates do not bite and no SDLT is payable.

For transfers between spouses or civil partners who are living together, there are also special rules in the SDLT regime that treat their dwelling interests on a combined basis when considering whether the purchaser owns other dwellings. That is why adding a spouse to a buy-to-let can potentially fall within the additional dwelling rules even though the transfer is between spouses.

Analysis

Step 1: identify whether there is a land transaction.

Adding a spouse to the legal title or beneficial ownership of a dwelling is normally a land transaction for SDLT purposes.

Step 2: identify the consideration.

If no money is paid, people sometimes assume there is automatically no SDLT. That is not always right. If the incoming spouse becomes liable for part of the mortgage, the assumed debt is treated as consideration.

Step 3: work out how much debt is actually being assumed.

This is crucial. If the total outstanding mortgage is about £33,000, the amount treated as consideration will usually be the share of that debt taken on by the incoming spouse. In many spouse transfers into joint names, that may be half of the mortgage debt, though the exact legal structure matters. On these facts, even the full mortgage balance mentioned is still below £40,000.

Step 4: consider the higher rates for additional dwellings.

Because the couple already own another home and the transferred property will be a buy-to-let rather than a replacement main residence for the incoming spouse, the higher rates question must be checked. For completions on or after 2 April 2025, the higher rates surcharge is 5%.

Step 5: apply the £40,000 minimum consideration threshold.

If the chargeable consideration for the transfer is less than £40,000, the transaction is not caught by the higher rates rules. If there is no other chargeable consideration, there will be no SDLT to pay.

Step 6: ignore the market value unless a specific rule requires it.

For this kind of transfer between spouses, the market value of the property, such as £200,000, is not the starting point for SDLT if the transfer is not for money. The relevant figure is usually the chargeable consideration actually given, here potentially the assumed mortgage debt. The property value matters commercially, but it does not itself create SDLT on a no-cash transfer.

Step 7: note that the original purchase history does not change the SDLT answer on the new transfer.

The fact that the property was once the couple’s home, and later became a buy-to-let, helps explain the background but does not itself determine the SDLT charge on the later transfer. The SDLT question is based on the facts at the time of the new transaction.

Outcome

On the facts described, the practical conclusion is that no SDLT should be payable if the only chargeable consideration is the spouse taking on mortgage debt and that debt is below £40,000.

That remains the likely outcome even though:

• the property is becoming a buy-to-let,
• the couple already own another home, and
• the higher rates for additional dwellings would otherwise be relevant.

The reason is that the mortgage-related consideration is below the £40,000 threshold.

The reported outcome in this scenario was that the transfer completed without SDLT being payable by the spouse.

Practical Steps

If you are assessing a similar transfer, check the following:

1. Confirm who currently owns the property and whether it is held personally or through a company.
2. Confirm whether the transfer is of legal title, beneficial ownership, or both.
3. Check the exact outstanding mortgage balance at completion.
4. Check what share of the mortgage debt the incoming spouse will legally assume.
5. Identify whether any cash or other consideration is being paid in addition to the mortgage assumption.
6. Consider whether the higher rates for additional dwellings would apply if the consideration were £40,000 or more.
7. Ensure the conveyancer or solicitor records the consideration correctly on the SDLT return, or confirms that no return is needed if the rules permit that result.
8. If the transfer is being done for income tax planning, also consider the separate income tax and beneficial ownership issues, including whether a declaration of trust and, where relevant, Form 17 may be needed.

If the property is said to be uninhabitable or not suitable for use as a dwelling, take care. The condition threshold is now relatively high following Amarjeet and Tajinder Mudan v The Commissioners for HMRC [2025] EWCA Civ 799. Minor defects, dated condition, or work needed to modernise will usually not be enough on their own.

Conclusion

Adding a spouse to a buy-to-let property can trigger SDLT if the spouse takes on mortgage debt, because that debt counts as consideration. But where the assumed debt is less than £40,000, there is generally no SDLT to pay, even if the property counts as an additional dwelling and the transfer completes on or after 2 April 2025.

Legal References Used

• Finance Act 2003, section 43
• Finance Act 2003, Schedule 3, paragraph 1
• Finance Act 2003, Schedule 4, paragraph 8
• Finance Act 2003, Schedule 4ZA
• Amarjeet and Tajinder Mudan v The Commissioners for HMRC [2025] EWCA Civ 799

This page was last updated on 22 March 2026.

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