How Stamp Duty Affects Your Mortgage Affordability
Stamp duty does not reduce your mortgage offer directly, but it reduces your available deposit — which changes your loan-to-value ratio and the rates lenders will offer you.
Key Takeaways
- •SDLT must be paid from your own funds — it cannot usually be added to the mortgage
- •Every pound spent on SDLT is one less pound in your deposit, raising your LTV
- •Moving from 85% to 90% LTV typically costs 0.3%–0.6% more on your mortgage rate
- •First-time buyers pay no SDLT under £300,000 — a significant affordability advantage
- •Lenders stress-test at higher rates, so a higher LTV can indirectly reduce maximum borrowing
In this article
How Lenders Factor SDLT Into Affordability
Mortgage lenders assess affordability primarily through income multiples (typically 4–4.5x annual income) and stress tests at a rate several percentage points above your actual rate. SDLT itself does not appear in this calculation — lenders do not reduce your maximum offer because you owe £7,500 in stamp duty.
The indirect effect is more significant. Your deposit determines your loan-to-value ratio, and lenders offer materially different rates depending on which LTV band you fall into. When SDLT is paid from your savings, the remaining deposit is smaller, the LTV is higher, and the mortgage rate is worse. A worse rate means monthly repayments are higher, which in turn means the lender's stress test — typically applied at a rate 2–3% above your product rate — allows you to borrow less.
Lenders also review your overall financial position. Many will ask for bank statements covering the last 3–6 months. If they see a large outgoing labelled 'stamp duty payment' shortly before your mortgage completes, this confirms your deposit has been partially consumed by SDLT — something underwriters note.
Important: If your SDLT payment will bring your LTV above a lender's product threshold (e.g. from 84% to 91%), you must disclose this honestly. Misrepresenting your deposit size is mortgage fraud.
SDLT Impact at Key Price Points
The table below shows a standard buyer (not first-time buyer) with exactly 10% of the purchase price saved, and how SDLT reduces the available deposit and raises the LTV:
| Purchase Price | Savings (10%) | SDLT Owed | Deposit Left | Actual LTV | Rate Impact |
|---|---|---|---|---|---|
| £250,000 | £25,000 | £2,500 | £22,500 | 91% | Higher tier |
| £350,000 | £35,000 | £7,500 | £27,500 | 92.1% | Higher tier |
| £500,000 | £50,000 | £15,000 | £35,000 | 93% | Significantly higher |
| £750,000 | £75,000 | £27,500 | £47,500 | 93.7% | Significantly higher |
Standard buyer (not FTB). SDLT: 2% on £125k–£250k, 5% on £250k–£925k. Assumes buyer has saved exactly 10% of purchase price.
This illustrates a critical problem: a buyer who believes they have a 10% deposit actually has a 7–8% deposit after paying SDLT. Most lenders require at least 5% deposit, but crossing the 90% LTV boundary triggers substantially higher rates and stricter criteria. Buyers at the price points above would need to find additional savings before exchanging contracts.
How SDLT Changes Your LTV Ratio
Loan-to-value ratio is the percentage of the property price you are borrowing. Lenders price their products in LTV tiers — typically at 60%, 75%, 80%, 85%, and 90%. Each step up costs more in interest rate, and the difference between tiers is not trivial.
| LTV Band | Typical Rate Range (Mar 2026) | Monthly Cost on £300k (25yr) |
|---|---|---|
| 60% LTV | 4.2%–4.7% | £1,614–£1,690 |
| 75% LTV | 4.4%–4.9% | £1,650–£1,726 |
| 80% LTV | 4.6%–5.1% | £1,688–£1,766 |
| 85% LTV | 4.8%–5.4% | £1,726–£1,820 |
| 90% LTV | 5.2%–5.9% | £1,804–£1,933 |
| 95% LTV | 5.7%–6.5% | £1,893–£2,025 |
Indicative rates for a 2-year fixed mortgage in England, March 2026. Actual rates vary by lender and individual circumstances.
The gap between 85% LTV and 90% LTV is roughly £100–£200 per month on a typical mortgage. Over a 25-year term, that difference compounds to tens of thousands of pounds. A buyer who has saved exactly enough to reach 85% LTV but then loses part of that deposit to SDLT — dropping to 90% LTV — will pay significantly more in interest over the mortgage term than the SDLT cost itself.
First-Time Buyer Advantage
First-time buyers in England pay no stamp duty on properties up to £300,000, and a reduced rate on properties up to £500,000. This is a substantial affordability advantage over standard buyers:
| Purchase Price | Standard SDLT | FTB SDLT | FTB Saving | LTV Benefit |
|---|---|---|---|---|
| £200,000 | £1,500 | £0 | £1,500 | Full deposit preserved |
| £275,000 | £3,750 | £0 | £3,750 | Full deposit preserved |
| £400,000 | £10,000 | £5,000 | £5,000 | 1.25% LTV improvement |
| £500,000 | £15,000 | £10,000 | £5,000 | 1% LTV improvement |
A first-time buyer purchasing at £300,000 keeps their entire deposit — every pound of their savings goes toward reducing their LTV. A standard buyer at the same price pays £5,000 in SDLT (2% on £125k–£250k, 5% on £250k–£300k), which directly reduces their deposit and raises their LTV. Read more on FTB SDLT relief.
Interactive Affordability Calculator
Enter your property price and total savings to see how SDLT affects your deposit and LTV ratio.
SDLT Due
£7,500
Deposit After SDLT
£42,500
Actual LTV
87.9%
LTV Increase
+2.1%
Rate band: Higher (≤90% LTV) — noticeably higher rates
Without SDLT, your LTV would have been 85.7% — a better tier.
Strategies to Reduce the Impact
Save an SDLT buffer separately
Keep your deposit and SDLT fund in separate savings pots. This prevents mental accounting errors and ensures you never accidentally deploy SDLT money as deposit.
Negotiate the purchase price
Buying just below an SDLT band threshold can save thousands. A property at £249,000 instead of £251,000 keeps you in the 2% band on the marginal amount rather than the 5% band, saving up to £600.
Use a Help to Buy ISA or Lifetime ISA bonus
A Lifetime ISA provides a 25% government bonus on up to £4,000 per year, which can be used toward a first home purchase. This bonus effectively offsets part of your SDLT bill by boosting your overall funds.
Consider a family gifted deposit
A gift from family can top up your deposit without affecting your SDLT liability. Read our guide on gifted deposits and stamp duty to understand the lender requirements.
Check your first-time buyer eligibility
Confirm your FTB status before budgeting. If you qualify, you pay zero SDLT under £300,000 — and your entire savings go toward your deposit. This can shift you from 90% LTV to 85% LTV at a single stroke.
Frequently Asked Questions
Does stamp duty reduce how much I can borrow?
Not directly — lenders calculate your maximum loan based on income multiples and stress tests, not on your SDLT bill. However, SDLT reduces your deposit, which raises your LTV, which leads to a higher interest rate. A higher rate means higher monthly costs, which in turn reduces what the lender's affordability model considers sustainable. The indirect effect is real, even if the mechanism is not a direct reduction.
Do lenders include stamp duty in their formal affordability assessment?
Most do not include SDLT in the formal income stress-test. They calculate affordability based on the mortgage amount, rate, and your income and commitments. However, savvy underwriters and mortgage advisers will flag situations where SDLT has materially eroded a deposit, and some lenders may ask for evidence of how the SDLT will be funded to ensure you have not secretly borrowed the money.
How much extra deposit do I need to account for stamp duty?
Budget for your full SDLT liability on top of your target deposit. Use our SDLT calculator to find the exact amount. As a rough guide: a standard buyer at £350,000 owes £7,500 in SDLT. If you want a 10% deposit (£35,000), you need £42,500 in savings — not £35,000. Always add a further buffer for legal fees, survey costs, and removals (typically £2,000–£5,000).
Ready to see your numbers?
Use our free calculator to see exactly how much stamp duty you need to budget for.
Calculate your stamp duty
Emma Richardson, MRICS
Chartered Surveyor & Property Tax Specialist
Emma Richardson is a RICS-qualified Chartered Surveyor with over 12 years of experience in UK property taxation. She founded Stamp Duty Calculator to help buyers understand the complex world of property transaction taxes.