Plan · Calculator 13
What will your mortgage really cost?
Calculate monthly payments, total interest and amortisation, then stress-test a rate change and compare repayment with interest-only borrowing.
1 Enter your figures2 Review assumptions3 Explore the result
Your figures
Your entries stay in this tab and are not sent to Money Considered. A shareable link includes only the assumptions shown in its URL.
Estimated monthly mortgage payment
£2,019/mo£382,500 repayment mortgage at 4.0% over 25 years.Mortgage amount£382,500£67,500 cash deposit
Loan-to-value85.0%15.0% deposit or equity
Total interest£223,193Across 25 years at a constant rate
If the rate changes from 4.0% to 6.0%
+£445/moThe modelled monthly payment becomes £2,464. Total interest changes by +£133,643 if that rate then remains constant for the full term.Hover over or focus a point to see its exact value.
Annual payment anatomy
How the payment changes the balance
Interest£15,134
Capital repaid£9,093
Balance after year 1£373,407
Term trade-off
A longer term lowers the payment but raises total interest.
Extending from 25 to 30 years reduces the modelled payment by £193 a month but adds £51,708 of interest.
Mortgage summary
The interest rate is held constant for the full term in each illustration.
| Scenario | Monthly payment | Total interest | Capital left |
|---|---|---|---|
| Repayment at 4.0% | £2,019 | £223,193 | £0 |
| Repayment at 6.0% | £2,464 | £356,836 | £0 |
| Repayment at 4.0% | £2,019 | £223,193 | £0 |
| Interest-only at 4.0% | £1,275 | £382,500 | £382,500 |
Assumptions used
- The entered rate is constant for the full term in each scenario.
- Interest is calculated monthly on the opening balance and payments are made monthly.
- A repayment mortgage pays all capital and interest by the end of the entered term.
- An interest-only payment covers modelled interest but leaves the original mortgage capital due at the end.
- Product fees, valuation and legal costs, early-repayment charges, overpayments and changing property values are excluded.
- This does not test mortgage eligibility or affordability.
A lender’s calculation can differ because of daily interest, payment dates, fees and product rules. Treat this as a planning illustration, not a mortgage quote.
Common questions
UK mortgage calculator FAQs
How are monthly mortgage repayments calculated?
For a repayment mortgage, the calculator finds the constant monthly amount that repays the mortgage capital and interest over the selected term. For interest-only, the monthly payment covers modelled interest while the original capital remains due at the end.
What happens if my mortgage rate rises from 4% to 6%?
Enter 4% as the mortgage rate and 6% as the rate-after-change scenario. The calculator shows the difference in monthly payment and total interest under the simplified assumption that each rate applies for the whole remaining term.
What is loan-to-value or LTV?
Loan-to-value is the mortgage amount divided by the property value. A £225,000 mortgage on a £250,000 property is 90% LTV. Real lenders use their own valuation and product criteria.
Why does a longer mortgage term cost more?
A longer term spreads capital repayment across more months, reducing the monthly payment. But interest is charged for longer, so total interest is usually higher when the rate and other assumptions are unchanged.
What is the difference between repayment and interest-only?
A repayment mortgage gradually pays down both interest and capital. An interest-only mortgage pays the interest but leaves the original capital to be repaid at the end using a credible repayment plan.
Does the mortgage calculator include fees?
No. Product, broker, valuation, legal and account fees are excluded. If a product fee is added to the mortgage, it increases both the amount borrowed and the interest charged.
Will a lender offer me the mortgage shown?
Not necessarily. The calculator estimates payments but does not assess income, spending, credit history, age, property eligibility or a lender’s affordability and stress-testing rules.
Why might my lender quote a different payment?
Lenders may calculate interest daily, use specific payment dates, include fees, apply promotional and follow-on rates or round differently. A formal mortgage illustration is the authoritative product-specific document.