A first-time buyer's stamp duty relief disappears entirely once the purchase price crosses £500,000 — a hard cliff, not a slope. The 5% surcharge on an additional property works the opposite way: it never disappears, never caps, and keeps climbing in a straight line at every price point we tested, from £300,000 to £1.5 million. For a buyer financing a second home or buy-to-let, that means the mortgage maths and the tax bill rise together, with no plateau in either.
The surcharge has no ceiling
Anyone buying an additional residential property in England pays the standard stamp duty rates plus a flat 5% surcharge on the whole purchase price, with no upper limit (HMRC, 2026). We ran the Homecost stamp duty calculator at five price points to confirm the surcharge amount is exactly 5% of price at every one:
| Purchase price | Additional-property SDLT | Standard (mover) SDLT | Surcharge amount |
|---|---|---|---|
| £300,000 | £20,000 | £5,000 | £15,000 |
| £500,000 | £40,000 | £15,000 | £25,000 |
| £750,000 | £65,000 | £27,500 | £37,500 |
| £1,000,000 | £93,750 | £43,750 | £50,000 |
| £1,500,000 | £168,750 | £93,750 | £75,000 |
Figures calculated with the Homecost stamp duty calculator against the live 2026 SDLT rate tables, 13 October 2026. The surcharge column is, by construction, exactly 5% of the purchase price at every row — there is no band, discount or cap that changes that ratio, which is the opposite of how first-time buyer relief is capped at £5,000 once a purchase passes £500,000.
What income it takes to reach each price point
Most UK lenders size a mortgage at around 4.5 times household income, a convention that reflects the Bank of England Financial Policy Committee's loan-to-income "flow limit" rather than a fixed rule every lender must apply (Bank of England, 2026). Combined with a deposit, the maximum price a household can reach rearranges to income = price × (1 − deposit %) ÷ 4.5 — the same formula behind our income ladder for the £300k–£500k first-time buyer relief band. Running the same five price points through that arithmetic:
| Price point | Income needed (10% deposit) | Cash deposit (10%) | Income needed (25% deposit) | Cash deposit (25%) |
|---|---|---|---|---|
| £300,000 | £60,000 | £30,000 | £50,000 | £75,000 |
| £500,000 | £100,000 | £50,000 | £83,333 | £125,000 |
| £750,000 | £150,000 | £75,000 | £125,000 | £187,500 |
| £1,000,000 | £200,000 | £100,000 | £166,667 | £250,000 |
| £1,500,000 | £300,000 | £150,000 | £250,000 | £375,000 |
Both the income bar and the surcharge climb together, in lockstep, at every price on the ladder: £500,000 to £1,500,000 is a 3x jump in price, and both the income needed at a 10% deposit (£100,000 to £300,000) and the surcharge (£25,000 to £75,000) also scale exactly 3x. Nothing bends.
The contrast with first-time buyer relief
That straight-line behaviour is the opposite of what happens on the first-time buyer side of the market. First-time buyer relief is worth exactly £5,000, flat, anywhere inside the £300,000–£500,000 band — and then falls to zero the moment a purchase passes £500,000, a cliff-edge rather than a taper. A first-time buyer's income requirement keeps rising past that point exactly as it does here, but the relief offsetting part of the tax bill does not: it simply stops. An additional-property buyer never hits an equivalent cliff. The surcharge is active from the first pound of price, so there is no threshold where it switches on, switches off, or caps out — only a ratio that holds at £300,000 and still holds, unchanged, at £1,500,000 and beyond.
Why this matters for second-home and buy-to-let buyers
None of this is a comment on whether a second home or buy-to-let purchase is a good idea at any given price — that depends on rental yield, personal finances and a buyer's own circumstances, not on the stamp duty bill in isolation. What the numbers above show is narrower and more mechanical: unlike a first-time buyer, whose tax relief can disappear entirely at a specific price point, an additional-property buyer's surcharge is fully predictable at any budget — always 5% of the purchase price, on top of the standard rate, with no cap to plan around.
Every figure above is a rule-of-thumb calculation from public rate tables and lending conventions, not a lending decision or a recommendation to buy. Actual affordability depends on a lender's own income multiple, credit assessment, existing debt, rental income treatment (for a buy-to-let mortgage) and stress-testing, all of which vary by lender and by applicant. Speak to a qualified mortgage adviser before acting on any of the numbers above.
Check your own numbers
Run a specific price through the stamp duty calculator with the additional-property surcharge applied, or test your own income and deposit on the mortgage affordability calculator. To see the full monthly cost behind a purchase in a higher-value market, open the true-cost view for a sample postcode such as SW1A 1AA in Westminster, or browse more Cost Intelligence guides.
Based on live Homecost stamp duty calculator output against the 2026 SDLT rate tables, and the Bank of England's published loan-to-income lending convention. See how we source our data.