Do I pay the stamp duty second-home surcharge if I keep my old house?

Yes — if completion day on your new main home happens while you still own your old one, you pay the 5% additional-property surcharge on the whole purchase price on top of standard SDLT, but you can reclaim the surcharge from HMRC using form SDLT16 if you sell the previous main residence within 3 years of the new purchase.

Why does HMRC charge the surcharge at all if I’m moving?

Because the SDLT higher rate is applied on the snapshot of your completion day, not on your long-term intention. On completion, if you own more than one residential property anywhere in the world and the new one isn’t replacing a property you’ve already sold, the 5% surcharge (raised from 3% on 31 October 2024) is added to every band. HMRC then lets you correct the situation with a refund if you actually dispose of the old main residence inside a three-year window.

The rules come from Schedule 4ZA of the Finance Act 2003. Two triggers matter:

On completion, you (or your spouse/civil partner jointly with you) own two or more residential properties globally worth £40,000+ each.
The new home is not replacing a main residence you already sold before completing.

If both triggers are met, the surcharge applies.

What does the bill actually look like?

Worked example — a couple buying a £400,000 new home while keeping their existing £280,000 flat as a let.

Band	Rate (standard)	Rate (with 5% surcharge)	Tax on £400k
£0–£125k	0%	5%	£6,250
£125k–£250k	2%	7%	£8,750
£250k–£400k	5%	10%	£15,000
Total standard SDLT			£7,500
Total with surcharge			£30,000

The £22,500 surcharge component is the number that HMRC lets you reclaim if the old home qualifies as a main residence and you sell within 3 years. Standard SDLT of £7,500 is not reclaimable — you’d have paid that anyway.

A couple moving into a new home with a 'sold' sign on the old property visible through the window — If you complete on the new home before selling the old one, the surcharge bill lands first — but can be reclaimed within three years.

Who counts as owning the old property?

HMRC uses a global, household-wide test:

You and your spouse/civil partner are treated as one unit. If either of you owns another residential property, both trigger the surcharge on the new joint purchase. This applies even if the new home is bought in one name only.
Overseas properties count. A holiday apartment in Spain worth £60,000 fully triggers the rule. Only properties worth under £40,000 are ignored.
Beneficial ownership counts, not just legal title. A property held via trust, where you’re the beneficial owner, counts.
Inherited shares count. If you inherited 25% of a family home worth £200,000+, that’s a £50,000+ interest — enough to trigger the surcharge on your new buy.
Buy-to-let properties are not main residences. The surcharge applies; you can’t reclaim by selling a BTL — only a former main residence qualifies for the refund.

How do you reclaim the surcharge?

The process:

Sell the previous main residence within 3 years of completing on the new home.
Within 12 months of the sale (or 12 months after the new home’s SDLT filing deadline — whichever is later), submit form SDLT16 to HMRC.
Include proof of the sale (solicitor’s completion statement), the SDLT return reference from the new purchase, and bank details for the refund.
HMRC typically processes refunds within 4–12 weeks.

The 3-year window is strict. Exceptional extensions apply only for very specific reasons (chain failure, delayed probate) — mis-selling your home’s timing is not accepted as grounds.

Our stamp duty calculator shows both “with-surcharge” and “reclaimable” figures for this scenario.

What if the chain breaks?

If you completed on the new home expecting to sell the old one the same week but the sale falls through, you’re stuck with the surcharge until you actually sell. You have the full 3 years — many chain-break situations still reclaim comfortably — but cash flow becomes the problem. Budget for carrying the surcharge for up to 3 years; in our £400k example above, that’s £22,500 tied up.

A bridging loan can cover the gap between completion and resale, but it’s expensive (typical 2026 bridging rates 0.75–1.0% per month) and only worth it where you can see the old home selling within 3–6 months.

The misconception that bites hardest

“I’m moving house, so it’s my main residence — no surcharge.” The moment of completion is what HMRC looks at, not your intention six weeks later. If you own two residential properties on the day of completion and neither was sold the same day or earlier, the surcharge applies. The reclaim process fixes this — but only if:

The old home was genuinely a main residence (not a BTL or a holiday let you stayed in occasionally).
You sell within 3 years.
You file SDLT16 in time.

The commonest trap is simultaneous completion not happening. If your buyer’s solicitor delays and the old sale completes on Friday but you complete on the new house on Thursday, you pay the surcharge. Talk to your conveyancer about synchronising completions — that alone can save tens of thousands on a bigger purchase.

This is information, not regulated advice. SDLT rules have been amended several times since 2024; confirm current status with HMRC or a conveyancer before completion.