Mortgage & Stamp Duty Calculator 2025/26

Reviewed by Mustafa Bilgic
UK Calculator Editor · Updated May 2026

Why combine the mortgage and SDLT calculations

Most UK buyers underestimate the cash they need on completion day because Stamp Duty Land Tax is paid separately from the deposit — your conveyancer asks for it 14 days after exchange in addition to your deposit funds. A combined view stops the nasty surprise of finding out at the last minute that you need £8,000 more than you thought.

On a £300,000 owner-occupier purchase the SDLT bill is £2,500 (5% of the £50,000 portion above the £250,000 threshold). Adding that to a £30,000 deposit means you need £32,500 cash, plus solicitor fees of around £1,800–£2,400 and a survey of £400–£900.

The calculator above lets you flex price, deposit, rate and term so you can see how the total cash requirement and monthly payment move together. The default rate of 4.5% reflects the Bank of England base rate at April 2026; high-street 5-year fixed rates were trading at 4.4–4.9% at the same point.

Standard SDLT bands for owner-occupiers in 2025/26

• 0% on the portion £0–£250,000
• 5% on £250,001–£925,000
• 10% on £925,001–£1,500,000
• 12% above £1,500,000

These rates apply to England and Northern Ireland and are charged on a sliced (banded) basis — only the portion in each band is taxed at that rate, not the whole purchase price. First-time buyer relief raises the 0% band to £425,000 (see the dedicated FTB calculator). Welsh and Scottish buyers use LTT and LBTT respectively, both of which use slightly different thresholds.

Example A: £210,000 starter flat, 90% mortgage

Megan buys a one-bed in Newcastle for £210,000 with a £21,000 deposit. SDLT is £0 because the price is below the £250,000 threshold. Loan is £189,000 over 25 years at 4.5% → monthly payment £1,051. Cash on completion: £21,000 deposit + £0 SDLT + £1,800 solicitor ≈ £22,800.

Example B: £450,000 family home, 80% mortgage

The Patel family buys a £450,000 home in Reading with a £90,000 deposit. SDLT: 5% × £200,000 (the slice above £250k) = £10,000. Loan £360,000 at 4.5% over 25 years → £2,001 per month. Cash on completion: £90,000 deposit + £10,000 SDLT + ≈£2,200 solicitor + £550 survey = £102,750.

Example C: £900,000 London upgrade

Marcus and Helen sell up and buy a £900,000 terrace in Wandsworth, putting £180,000 down. SDLT: 5% × £675,000 = £33,750. Loan £720,000 at 4.5% over 25 years → £4,003 per month. Cash on completion: £180,000 + £33,750 + £3,200 solicitor + £900 survey ≈ £217,850.

Common mistakes to avoid

• Forgetting that SDLT is on top of the deposit — not financed into the mortgage.
• Applying the surcharge or first-time-buyer relief to the wrong category — the calculator above is the standard owner-occupier path only.
• Assuming the whole purchase price is taxed at the highest band — SDLT is sliced, not flat.
• Using the SDLT figure for properties in Scotland or Wales — those countries use LBTT and LTT.
• Quoting the asking price instead of the agreed purchase price; SDLT is on the price actually paid.

When to use this calculator

Run the numbers when you receive a mortgage in principle, when an offer is accepted, and again after survey if you renegotiate. Buyers planning a 5-year fix should also re-run with a 1–2% higher rate to stress-test affordability.

How this differs in Scotland, Wales and Northern Ireland

Standard SDLT applies in England and Northern Ireland only. Welsh purchases use Land Transaction Tax with a higher £225,000 main threshold and slightly different band edges. Scottish purchases use Land and Buildings Transaction Tax, with a £145,000 main residence threshold and a 6% band above £750,000.

When this calculator is and isn't the right tool

The Mortgage & Stamp Duty Calculator 2025/26 above is built for the most common UK 2025/26 scenarios in this tax area. It will be the right tool when your situation maps cleanly onto the inputs — single property or simple aggregation, standard HMRC rates and bands, and individual taxpayer (rather than complex trust or partnership structures). It is informational and does not replace tailored advice from a chartered tax adviser, especially for transactions above £500,000, cross-border situations, or where reliefs interact with each other. For year-end filings, always reconcile with HMRC's own free calculators on gov.uk before pressing submit on Self Assessment.

Closely related calculators

• Mortgage and Stamp Duty Calculator UK — useful when you need a different angle on the same UK property tax topic, especially if your situation involves multiple types of property income or disposal.
• Mortgage Calculator with Stamp Duty — useful when you need a different angle on the same UK property tax topic, especially if your situation involves multiple types of property income or disposal.
• First-Time Buyer SDLT Calculator — useful when you need a different angle on the same UK property tax topic, especially if your situation involves multiple types of property income or disposal.
• Total Property Purchase Cost — useful when you need a different angle on the same UK property tax topic, especially if your situation involves multiple types of property income or disposal.
• UK Stamp Duty Rates 2026 — useful when you need a different angle on the same UK property tax topic, especially if your situation involves multiple types of property income or disposal.

Glossary of UK property tax terms

SDLT

Stamp Duty Land Tax — the UK government tax on residential property purchases in England and Northern Ireland.

HRAD

Higher Rates for Additional Dwellings — the formal name for the 5% surcharge on second homes and BTL purchases.

SDLT1

The HMRC return form filed within 14 days of completion to declare and pay SDLT.

Sliced bands

SDLT is charged on slices of the price within each band, not on the whole price at the highest band.

Effective rate

Total SDLT divided by the purchase price, expressed as a percentage.

Section 24

The 2017 rule replacing full mortgage interest deduction with a 20% tax credit for individual residential landlords.

SA105

The Self Assessment supplementary form for UK property income.

Box 44

The SA105 box for residential property finance costs (mortgage interest).

Property allowance

£1,000 tax-free band for individual property income, claimable instead of expenses.

Rent-a-Room scheme

Separate £7,500 allowance for letting a furnished room in your main home.

Tax planning checklist

1. Confirm the figures input above match your actual position — purchase contract, mortgage offer or completion statement.
2. Cross-check the year (2025/26) — figures change every April. The tax year 2026/27 starts 6 April 2026.
3. Use HMRC's official calculator at gov.uk for the final filing figure; this calculator is informational.
4. Keep records for at least 6 years — HMRC's normal enquiry window. 21 years for fraud investigations.
5. Discuss any unusual transaction (joint purchase, gift, divorce settlement, trust) with a qualified tax adviser.
6. Submit your return online via Government Gateway — paper deadlines are earlier and penalties harsher.