Cohabiting Couples and Stamp Duty

How HMRC Treats Unmarried Couples

Married couples and civil partners are treated as a single unit for stamp duty purposes. If your spouse owns a property, HMRC considers that you also have an interest in residential property. This rule does not apply to unmarried couples.

If you are cohabiting but not married or in a civil partnership, HMRC assesses each partner's property ownership separately. Partner A's ownership history has no bearing on Partner B's stamp duty position, provided they are purchasing independently.

This means an unmarried couple has a significant structural advantage: one partner can buy a property as a first-time buyer (claiming relief and avoiding the surcharge) even if the other partner already owns a home. The same purchase by a married couple would lose both benefits.

The distinction matters most when one partner owns a home and the couple wants to buy a new property together. The approach you choose (joint purchase, sole purchase, or a combination) has a direct impact on the stamp duty bill.

When One Partner Already Owns Property

This is the most common scenario for cohabiting couples: Partner A owns a flat or house, and the couple now wants to buy a home together. The stamp duty outcome depends entirely on whose name goes on the title deeds of the new property.

If Partner A sells their existing property before completing on the new joint purchase, the surcharge can be avoided. However, timing is critical: the sale must complete before or on the same day as the new purchase. If Partner A still owns the old property at the point of completion, the surcharge applies regardless of whether a sale is in progress.

For more on the replacement main residence rules and the 36-month refund window, see our replacement main residence guide.

Buying Jointly: Surcharge Risk

When two people buy a property together, HMRC applies the highest applicable rate to the entire purchase. If either buyer already owns residential property (and it is not being replaced), the 5% additional dwelling surcharge applies to the whole transaction, not just to that person's share.

This catches many cohabiting couples off guard. Partner B may never have owned property, but because Partner A is on the deed and already owns a flat, the surcharge applies to the entire purchase price.

The surcharge also eliminates any first-time buyer relief. For FTB relief to apply, all purchasers must be first-time buyers. If Partner A has ever owned property, neither partner can claim FTB relief on the joint purchase. See our first-time buyer guide for the full eligibility rules.

Keeping It in One Name

The simplest way to avoid the surcharge is for Partner B (the non-owner) to buy the new property in their sole name. This preserves FTB relief (if eligible) and avoids the surcharge entirely. Partner A's existing property is irrelevant because Partner A is not a purchaser.

The practical challenge is mortgage affordability. If Partner B cannot qualify for a mortgage large enough to buy the property alone, the couple may need a joint mortgage. However, being on the mortgage is not the same as being on the title deeds:

• Some lenders offer Joint Borrower Sole Proprietor (JBSP) mortgages where both incomes count but only one person owns
• Partner A can act as a guarantor on Partner B's mortgage without being on the deeds
• Some lenders require all borrowers to be on the title deeds, which would trigger the surcharge

Speak to a mortgage broker before deciding. The right mortgage product can save thousands in stamp duty. See our helping children buy guide for a detailed comparison of JBSP and guarantor mortgages.

Tenants in Common vs Joint Tenants

If you do decide to buy jointly, you will choose between two forms of co-ownership: joint tenants or tenants in common. Neither form changes the stamp duty outcome, but they have different consequences for inheritance and separation.

For unmarried couples, tenants in common is generally recommended because it allows each partner's financial contribution to be recorded. If one partner contributed 80% of the deposit, their share can reflect that. This has no stamp duty consequence but provides important legal protection if the relationship ends.

Worked Example: Joint vs Sole Purchase

Partner A owns a flat. Partner B is a first-time buyer. They want to buy a £400,000 home together.

The £25,000 saving comes from two sources: avoiding the 5% surcharge (£20,000) and claiming FTB relief instead of standard rates (£5,000 saving). Use our first-time buyer calculator and second home calculator to see the exact figures for your property price.

Moving in Together After Buying Separately

A related scenario: both partners already own separate properties and now want to live together. If one partner moves into the other's home, no stamp duty is triggered because there is no property transaction.

However, the partner who moves in may now own a property they no longer live in. If they later sell it, any future property purchase will be assessed based on whether they still own the vacated property at the point of completion.

If the couple wants to sell both properties and buy a new home together, the timing matters. If both existing properties are sold before or on the day of the new joint purchase, no surcharge applies because neither partner owns additional property at the point of completion.

If only one property has been sold by completion day, the partner who still owns their old property triggers the surcharge on the joint purchase. The 36-month refund rule then allows a refund if the remaining property is sold within 36 months.