Do you pay higher rate SDLT when buying out a co-owner in your main home if you already own a buy-to-let?

Introduction

This is a common SDLT question where someone already lives in a property, owns part of it, and wants to buy out another family member’s share. The confusion usually comes from the fact that the property being acquired is the buyer’s main home, while the other property they own is a rental property. Many people assume the surcharge should somehow attach to the rental property instead. That is not how the SDLT rules work.

The key issue is whether, at the effective date of the transaction, the buyer already owns another dwelling and whether the transaction counts as a replacement of their only or main residence. If it does not count as a replacement, the higher rates for additional dwellings can apply even though the property being acquired is the home the buyer already lives in.

The Question

A married couple already own a minority share in the home they live in. Another family member owns the remaining majority share. The couple now want to buy that remaining share so that they own the whole property and continue living there as their main residence.

Separately, one spouse also owns a long-held buy-to-let property which has always been rented out and has never been used as the couple’s home.

The question is whether the purchase of the remaining share in the main home should be charged at normal residential SDLT rates, on the basis that it is the couple’s main residence, or whether the higher rates apply because they also own the rental property.

Nick’s Explanation

Nick’s core point was that SDLT looks at the transaction being completed and the buyer’s property position at that time. It does not allow the surcharge to be treated as if it belongs to the rental property instead of the home being acquired.

In anonymised form, his reasoning was:

“You are acquiring a chargeable interest in a dwelling. If, at completion, you already own another dwelling and you are not replacing your only or main residence, the higher rates apply.”

He also explained that buying a further share in the same home is not the same as replacing a previous main residence. There is no disposal of an old main residence and no acquisition of a new one. Instead, there is simply an increase in the ownership share of the existing home.

On that basis, the higher rates would apply to the purchase of the remaining share if the buy-to-let is still owned personally at completion.

Nick then identified a possible planning route: if the rental property ceased to be owned beneficially by the couple before completion of the buy-out, the surcharge position on the main-home transaction could change. He mentioned two broad possibilities in principle:

• transfer of the rental property to a company before the main transaction completes; or
• transfer into a trust where the couple are no longer the beneficial owners.

But he also made clear that if the rental property remains in personal ownership at the point of completion, the higher rate SDLT charge on the buy-out will apply.

The Law

SDLT is charged on land transactions under section 42 of the Finance Act 2003. Under section 43, a land transaction includes the acquisition of a chargeable interest in land. Buying an additional share in a dwelling is an acquisition of a chargeable interest, so it falls within SDLT.

The higher rates for additional dwellings are contained in Schedule 4ZA to the Finance Act 2003.

In broad terms, the higher rates apply if, at the end of the day of the transaction:

• the buyer has a major interest in the dwelling being acquired;
• the consideration is at or above the relevant threshold;
• the buyer owns a major interest in another dwelling worth at least the minimum amount required by the legislation; and
• the purchased dwelling is not a replacement for the buyer’s only or main residence.

The replacement of only or main residence rules are especially important. Schedule 4ZA provides relief from the surcharge where the buyer disposes of a previous only or main residence and acquires a new only or main residence. The legislation is concerned with replacement, not with improving or increasing ownership of the same residence.

So if a buyer keeps their existing main home and simply acquires a further share in it, that does not normally amount to replacing a main residence.

Analysis

Step 1: there is a chargeable transaction.

Buying the remaining share from the co-owner is a land transaction for SDLT purposes. It does not matter that the buyers already own part of the property. SDLT can still arise on the additional share being acquired.

Step 2: the buyers already own another dwelling.

If one spouse owns a buy-to-let, that can count for higher-rate SDLT purposes. For married couples and civil partners living together, the Schedule 4ZA rules generally treat them as a unit when testing additional dwelling ownership. In practice, one spouse’s additional property can bring the surcharge into play for the transaction.

Step 3: ask whether the purchase is a replacement of only or main residence.

Here, the couple are not selling an old home and moving to a new one. They are staying in the same property and buying a larger share in it. That means the replacement test is not satisfied.

Step 4: the surcharge applies to the transaction being completed.

This is the point that often feels counterintuitive. The SDLT higher rates are not a tax charged retrospectively on the rental property. They are higher rates applied to the current acquisition because, at that moment, the buyers already own another dwelling and are not replacing their main residence.

So the argument that “the let property should carry the higher rate, but the main residence should be taxed normally” does not fit the legislation. SDLT is charged transaction by transaction. The rates for the current purchase are determined by the buyer’s overall position at completion.

Step 5: could planning before completion change the result?

Potentially, yes. If before completion the buyers genuinely cease to own the rental property beneficially, then at the time they acquire the remaining share in their home they may no longer meet the additional dwelling condition.

That said, each route has its own tax and legal consequences:

• a transfer to a company is itself a separate land transaction and can trigger SDLT based on market value, with the higher rates usually applying to the company acquisition;
• a trust arrangement may alter beneficial ownership, but it is technically complex and can have wider tax implications.

It is also important not to assume that a transfer to a connected company or trust is tax-neutral overall. SDLT, capital gains tax, financing issues, lender consent, company law and trust law all need to be checked together.

One point in the source explanation should be treated with caution: a transfer at market value does not automatically mean there is no capital gains tax. For CGT purposes, transfers to companies and many connected-party transactions can be deemed to take place at market value anyway, and a gain may arise depending on base cost, reliefs and structure. That issue sits outside the SDLT question but is important in practice.

This is not an “uninhabitable” or “not suitable for use” case, but for completeness readers should note that those condition thresholds are now relatively high following Amarjeet and Tajinder Mudan v The Commissioners for HMRC [2025] EWCA Civ 799.

Outcome

If a buyer is purchasing an additional share in the home they already occupy, and at completion they still personally own another dwelling such as a buy-to-let, the higher rates of SDLT will usually apply.

The fact that the acquired property is the buyer’s main residence does not by itself prevent the surcharge. The key reason is that the buyer is not replacing a previous only or main residence.

So, in a case like this, the conveyancers’ view that higher rate SDLT applies is likely to be correct if the rental property remains in personal ownership at completion.

Practical Steps

If you are in a similar position, work through the following points before exchange or completion:

1. Confirm exactly who owns each property, both legally and beneficially.
2. Check whether you and your spouse or civil partner are treated together under Schedule 4ZA.
3. Identify whether the transaction is truly a replacement of only or main residence, or merely an acquisition of a further share in the same home.
4. Calculate SDLT on the buy-out both at standard rates and at higher rates.
5. If considering pre-completion restructuring, obtain advice on SDLT, CGT, trust law, company law and mortgage consent before taking any step.
6. Make sure any restructuring completes before the main-home transaction if the plan depends on changing the ownership position for SDLT purposes.
7. Keep clear records of ownership, occupation, valuations and transaction timing.

Conclusion

Buying out a co-owner in your main home can still attract higher rate SDLT if you already own another dwelling and are not replacing your only or main residence. The surcharge applies to the transaction being completed, not to whichever property feels like the “additional” one in everyday terms. In most cases, increasing your share in the same home is not a replacement of residence, so the higher rates apply unless your ownership position has changed before completion.

Legal References Used

• Finance Act 2003, section 42
• Finance Act 2003, section 43
• 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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