Stamp duty surcharge: your spouse's home vs your old one

At the England median sale price of £300,000, the same buyer can owe £5,000, £20,000, or £0 in Stamp Duty Land Tax — before their income, deposit or credit profile is even considered. The difference is decided by two rules that sit a few pages apart in the same piece of legislation and pull in opposite directions.

The first rule can attach a property you do not own to your name. The second can let you ignore a property you do. Both live in Schedule 4ZA of the Finance Act 2003 — the schedule that governs the 5% surcharge on "additional dwellings". Which one applies to a given purchase is the difference between the standard bill and a bill several times larger.

This piece explains how the two tests work, using figures calculated for a £300,000 purchase in England on 6 July 2026. It is general information about how the rules are written, not advice about any individual transaction.

The surcharge in one line

England and Northern Ireland charge residential SDLT in slices (rates from 1 April 2025):

When a purchase counts as an additional dwelling, a surcharge of 5% is added to every slice (the surcharge rose from 3% to 5% on 31 October 2024). Because it applies across the whole price rather than a single top slice, the surcharge works out as a flat 5% of the purchase price:

Figures from the Homecost stamp duty calculator, 6 July 2026, England rates. The whole question, then, is whether a purchase is an "additional dwelling" at all. That is where the two tests come in.

Test one — paragraph 9: your spouse's home is treated as yours

The intuitive version of the surcharge is "you already own a home, so your next one is additional". But if you are married or in a civil partnership, the rules do not test you in isolation.

Paragraph 9 of Schedule 4ZA treats spouses and civil partners who are living together as a single unit. If you buy a property on your own, and your spouse or civil partner — who is not a buyer on the paperwork — owns a major interest in another dwelling, that dwelling is treated as though you owned it. Your solo purchase can therefore be an additional-dwelling purchase even though the title deeds of the other property carry only your partner's name.

Worked at the £300,000 median, this is the gap between two numbers:

The £15,000 swing turns entirely on a property the buyer has no legal interest in. The same mechanism is what can quietly cancel first-time buyer relief for the partner who has genuinely never owned a home — a scenario covered in how spouse aggregation cancels first-time buyer relief.

There is one carve-out built into the same paragraph. Spouses and civil partners are treated as living together unless they are separated under a court order, under a deed of separation, or in fact separated in circumstances likely to be permanent. Where that permanence test is met at the effective date of the transaction, the partner's dwelling is not attributed — which is why marital status and the timing of a separation can change the answer. The evidential side of that is set out in the SDLT treatment of separating couples.

Test two — paragraph 3: replacing your only or main residence

The second rule runs the other way. Paragraph 3 sets out when a single-dwelling purchase is a higher-rates transaction, and it contains an exception: the surcharge does not apply where the property being bought replaces the purchaser's only or main residence.

In plain terms, if you are selling the home you live in and buying a new one to live in, you are not adding a dwelling to a portfolio — you are swapping one main residence for another. You can own several other properties and still fall outside the surcharge on that purchase, provided the new home genuinely replaces the old main residence and your previous main residence has been disposed of.

So the same buyer who would pay £20,000 under paragraph 9 aggregation could pay the standard £5,000 if the purchase qualifies as a replacement — the property their spouse owns stops being decisive once the new home is a like-for-like replacement of the couple's main residence that has been sold.

When both could apply, the order of sale decides

The interesting cases are the ones where both tests are in play — a couple who own a second property between them, selling their main home and buying another to live in. Here the sequence matters:

• Old home sold on or before completion of the new one. The replacement condition is satisfied at the effective date, so the standard rate applies straight away — £5,000 on a £300,000 purchase.
• New home bought before the old one is sold. At completion the buyer still owns both, so the surcharge is due upfront — £20,000 — and can be reclaimed once the previous main residence sells within the time limit set out in the rules. The mechanics of that repayment are covered in the additional-property surcharge refund route.

The cash-flow difference between paying £5,000 and fronting £20,000 to reclaim later is the practical reason the order of sale matters, even where the eventual tax position is identical. Conveyancers confirm which route applies on the facts of each completion.

The evidence is the same discipline, different documents

Both tests are decided on evidence, and the standard is the same: contemporaneous, dated, and ideally from a third party rather than the buyer's own later account. But the two rules call for different document sets, because they are proving different things:

• Replacement (paragraph 3) turns on the disposal of the old home — completion statements, the Land Registry entry for the sale, and dates that line up with the new purchase.
• Separation (paragraph 9) turns on the state of a relationship — a court order, a deed of separation, or a documented pattern showing the separation is likely to be permanent at the effective date.

Neither test rewards a story told after the fact. The paperwork that decides them is generated at the time, which is why the sequence of sale, completion and any separation is worth understanding before rather than after a purchase. For the fuller checklist on the separation side, see the evidence checklist for the spousal rule.

See the numbers for a real street

The bands above are national, but the price they land on is local. You can see the recent sale prices — and the standard SDLT that would apply — for any postcode using the Homecost tool: try a Birmingham postcode such as B1 1AA, which sits close to the England median, to see how the £250,000 and £925,000 thresholds fall across a real street.

For the wider picture on when the surcharge applies, the additional-property stamp duty surcharge guide works through the full set of conditions, and you can browse the rest of the cost intelligence guides for related breakdowns.

Based on 699,844 England residential transactions recorded in HM Land Registry Price Paid data for 2025 (median £300,000) and the 2026 England SDLT rate tables — see how Homecost sources its figures.

This article explains how the rules are written; it is not tax or legal advice, and eligibility for either test depends on the specific facts of a transaction. Speak to a qualified adviser before acting.