UK Mortgage Calculator
Work out what a UK monthly mortgage payment looks like during the fixed-rate period and after it reverts to the lender's Standard Variable Rate. Stamp duty and upfront costs are shown alongside the monthly number so you can see the whole picture.
Explain like I'm 5 (what even is this calculator?)
A mortgage is a big loan used to buy a house. In the UK, you usually agree a fixed rate for 2, 3 or 5 years, and your monthly payment stays the same during that time. When the fix ends, the rate changes to whatever the lender has set, which is almost always higher. This tool shows both numbers, plus the stamp duty bill and the cash you'll need on day one.
Calculate
Enter your numbers, then press Calculate.
Monthly breakdown
- During the fix (years 1–5)—
- After revert to SVR—
- Buildings insurance—
- Ground rent—
- Service charge—
- Total during fix—
- Total after SVR—
Upfront costs
- Deposit—
- Stamp duty (SDLT)—
- Product fee (if paid upfront)—
- Cash needed on completion—
Life of loan
- Loan principal—
- Balance at end of fix—
- Total interest (full term)—
- Total cost (principal + interest)—
Prove it
Monthly principal and interest use the standard formula M = P · r · (1 + r)n ÷ ((1 + r)n − 1), amortised across the full term at the initial rate. The balance at the end of the fix is the amortisation identity B = P(1+r)k − M((1+r)k − 1)/r. The SVR monthly is recalculated on that remaining balance over the remaining term. SDLT uses the 2025/26 England & Northern Ireland bands; Scotland (LBTT) and Wales (LTT) have different rules.
What the tool cannot know: your lender's actual SVR when the fix ends (it could be higher or lower than you type), rate changes during any tracker period, overpayments you choose to make, early repayment charges if you remortgage mid-fix, and lender-specific stress tests.
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How a UK mortgage actually works, in plain English
A UK mortgage has three moving parts that most calculators quietly skip over: the fixed-rate period, the Standard Variable Rate that kicks in when it ends, and the one-off costs on completion day. Getting all three on one page is the difference between a useful estimate and a misleading one.
The fixed-rate period
You agree an interest rate for a set period, most commonly 2, 3 or 5 years. During that window your monthly payment is locked. The rate you get depends on your deposit size (loan-to-value), your credit file, and the lender's pricing on the day you apply. Longer fixes usually cost slightly more in rate, but give you certainty for longer.
The revert to SVR
When the fix ends, the loan reverts to the lender's Standard Variable Rate unless you remortgage to a new deal. SVR is set by the lender and moves more or less in line with the Bank of England base rate, but with a generous margin added on. It is almost always a worse rate than any fix you could arrange, which is why most borrowers remortgage every time a fix ends. The calculator shows your payment on SVR so you can see the cliff edge.
Stamp Duty Land Tax
SDLT is a one-off tax on the purchase price, paid within 14 days of completion. Everyone pays SDLT in England and Northern Ireland. First-time buyers buying a home of £500,000 or less get relief: no SDLT on the first £300,000, then 5% on the slice between £300,000 and £500,000. Above £500,000, first-time buyers pay the standard rates. Scotland and Wales have their own equivalents (LBTT and LTT) with different bands; this calculator covers SDLT only, and dedicated LBTT and LTT tools are on the roadmap.
Product fees
Most fixed-rate deals come with an arrangement or product fee, typically £999 to £1,999. You can usually choose to pay it at completion or add it to the loan. Adding it to the loan feels easier but means you pay interest on the fee for the whole term, so it costs you meaningfully more over time. The calculator lets you toggle between the two so you can see the difference.
Leasehold extras
If the property is leasehold (common for flats and some new-build houses), you will also pay ground rent and a service charge. Neither is part of the mortgage, but both hit the same bank account every year, so the calculator pulls them into the monthly total.
Why the number you see here is a starting point, not an offer
A real mortgage offer depends on things this page cannot see. Your income and the way you earn it (salary, self-employed, commission). Your existing credit commitments. Your deposit source. Whether the property is a standard construction or something lenders treat cautiously. Whether you'd pass the lender's affordability stress test at a much higher notional rate. A broker takes all of that into account and can get you a rate the calculator doesn't know about, because it never hits the comparison sites.
Treat the figures on this page as the conversation starter. The conversation itself belongs with a qualified broker or directly with the lender.
What this tool does not do
It does not quote you a rate. It does not include conveyancing, survey, valuation, or broker fees, which typically add £1,500 to £3,000 on top of everything else. It does not handle help-to-buy, shared ownership, buy-to-let, Islamic mortgages, or bridging loans. It assumes you keep the same mortgage from day one to the end of the term, which almost nobody actually does, because remortgaging every fix period is the norm. It covers England and Northern Ireland stamp duty only.
Nothing on this page is financial advice. Every figure is an indication. For a real decision, speak to a qualified UK mortgage broker who can see the full picture.
Related calculators
The mortgage is one slice. These cover the rest of the buying and letting sums.
Frequently asked questions
How does a UK fixed-rate mortgage work?
You lock your interest rate for a set period, typically 2, 3 or 5 years. During that time your monthly payment is the same every month. When the fix ends, the loan reverts to the lender's Standard Variable Rate, which is usually higher, so most borrowers remortgage to a new fix.
What is Stamp Duty Land Tax?
A one-off tax on property purchases in England and Northern Ireland, charged in bands on the purchase price. First-time buyers pay no SDLT on the first £300,000 of a property costing up to £500,000. Scotland uses LBTT and Wales uses LTT, both with different bands.
Should I add the product fee to my loan?
Adding the fee to the loan is easier on completion-day cash, but you pay interest on that fee for the whole mortgage term, so it costs you more over time. Paying it upfront costs more on day one but less over the life of the loan. Toggle the option to see the difference.
Does this calculator send my numbers anywhere?
No. Everything runs in your browser. The numbers you type never leave your device.