UK mortgage calculators
Twelve calculators built for UK rules — SDLT, stress tests, Section 24, fixed-term breaks — with AI explanations of what your numbers actually mean.
All mortgage calculators
From your first affordability check to overpaying your final balance — every UK mortgage decision in one place.
Mortgage payment
Monthly cost, total interest, full amortisation schedule
Mortgage affordability
How much will a UK bank lend you against your income
Mortgage overpayment
Interest saved, years off the term, overpay vs invest
Stamp Duty
SDLT in England, LTT in Wales, LBTT in Scotland
Remortgage
Compare your fix end with new offers and SVR
Mortgage vs rent
Find the break-even year for buying over renting
Buy-to-let yield
Net rental yield after Section 24 and agent fees
Early repayment charge
Cost of leaving your fix before the end date
Joint borrower sole proprietor
Parents on the mortgage, but not on the deeds
LISA exit penalty
25% charge if you buy a home above £450k
Bridging loan cost
Interest plus exit fees on a 6-12 month bridge
Shared ownership staircasing
Cost of buying more of your own home over time
About mortgage calculators on Calclens
Calclens builds UK mortgage calculators that go one step further than the rest of the web — every result comes with a plain-English AI explanation, generated on demand. The calculation runs instantly in your browser. The AI layer is optional.
UK mortgages aren’t like US mortgages. They use fixed-term deals (typically 2, 3 or 5 years), Bank of England base rate influences SVR, Stamp Duty has different rules in England, Wales and Scotland, and buy-to-let landlords lost most of their mortgage interest relief under Section 24. Generic global calculators miss all of this. Ours don’t.
What makes these mortgage calculators different
- UK-first rules — SDLT bands for England and Northern Ireland, LTT for Wales, LBTT for Scotland, first-time buyer relief built in
- Honest yield maths — the buy-to-let calculator applies Section 24, not the older mortgage interest deduction most online tools still show
- AI explanation layer — powered by Claude (Anthropic), explained in detail on the how AI works page
- Free forever — no sign-up, no accounts, no display ads, no affiliate links
- Built in public — formulas come from HMRC, the Bank of England and FCA-authorised lender rate tables, documented on our methodology page
Which mortgage calculator should I use?
I’m a first-time buyer. Where do I start?
Start with the mortgage affordability calculator to find out how much a UK bank will lend you under current stress tests. Then use Stamp Duty to check first-time buyer relief on your target property. The mortgage payment calculator shows what the monthly figure looks like, and if you’re using a Lifetime ISA towards the deposit, check the LISA exit penalty calculator for the £450k purchase cap.
My fixed rate is ending. What now?
Use the remortgage calculator to compare your current deal versus new fixes or your lender’s SVR. If you’re thinking of leaving the fix early, check the early repayment charge first — it can wipe out the saving.
I have spare cash. Should I overpay my mortgage?
The mortgage overpayment calculator shows how much interest you’d save and how many years you’d knock off the term. The AI explanation compares it directly against putting the same money into a Stocks and Shares ISA, so you can see which option wins for your scenario.
Should I buy or keep renting?
The mortgage vs rent calculator finds your break-even year — the point at which buying becomes cheaper than renting in your area, accounting for deposit lost to opportunity cost, maintenance, and Stamp Duty.
I’m thinking of a buy-to-let. What’s the real return?
The buy-to-let yield calculator works out your net yield after mortgage interest, agent fees, voids and Section 24 — the rule that strips your mortgage interest relief if you own in your own name. Most quick yield numbers online ignore Section 24 and overstate the return.
My parents want to help. What are the options?
If parents help with affordability but won’t live there, a Joint Borrower Sole Proprietor mortgage adds their income to the application without putting them on the deeds. The JBSP calculator shows how much you can borrow combined and what it means for their tax and inheritance position.
Are these figures financial advice?
No. The calculators give you working numbers based on current UK rules — HMRC bands, lender stress test conventions, Bank of England rate data. The AI explanation provides context, not regulated advice. For a binding decision on a mortgage product, speak to an FCA-authorised mortgage broker.