Mortgage Calculator
Estimate your monthly mortgage payment and lifetime interest in seconds — free and private.
This mortgage calculator estimates your monthly repayment from three inputs: the amount borrowed, the annual interest rate, and the term in years. It uses the standard amortization formula that lenders use for repayment mortgages, and shows the total you would repay and how much of that is interest.
Those totals are usually the eye-opener. On a 200,000 loan at 5% over 25 years, the monthly payment is about 1,169 — but the total repaid is roughly 350,750, meaning around 150,750 goes to interest. Seeing that split makes it much easier to weigh a shorter term, a bigger deposit, or a lower rate against each other.
The calculator is free, requires no personal details, and everything is computed in your browser — nothing is sent to any lender or server.
How to estimate a mortgage payment
- Enter the loan amount — the property price minus your deposit.
- Enter the annual interest rate you expect or have been quoted.
- Set the term in years (25 is a common starting point).
- Read the monthly payment, total repayment, and total interest — figures update as you type.
- Try different terms and rates to see how each one moves the monthly cost and lifetime interest.
What the estimate includes — and what it leaves out
The formula covers principal and interest on a standard repayment mortgage with a fixed rate. Real mortgage costs often include more: arrangement and valuation fees, insurance, property taxes, and rate changes when a fixed period ends. Interest-only mortgages work differently again — the payment covers only interest and the balance never falls.
Use the result to compare scenarios and sanity-check affordability, then get an exact quote from a lender or broker, whose figure will reflect fees, your credit profile, and the specific product.
How the monthly payment is calculated
The calculator uses the standard amortization formula, M = P × r(1+r)ⁿ ÷ ((1+r)ⁿ − 1), where P is the amount borrowed, r is the monthly interest rate (the annual rate divided by 12), and n is the total number of monthly payments (the term in years times 12). It is the same equation lenders use for repayment mortgages.
The result is a level payment: the same amount every month for the whole term. Early on, most of each payment is interest and only a little chips away at the balance; as the balance shrinks the split gradually flips, until the final payments are almost entirely principal. That shifting mix is what amortization describes.
A worked example
Borrow 200,000 at 5% annual interest over 25 years. The monthly rate is about 0.4167% and there are 300 payments, which the formula turns into a monthly figure of roughly 1,169. Multiply that by 300 and you repay around 350,750 in total.
Subtract the original 200,000 and about 150,750 of that is pure interest — more than three-quarters of the amount you borrowed, paid on top. Seeing the split laid out like this is usually what prompts people to test a shorter term or a larger deposit.
How term, rate and amount move the number
The three inputs pull in different ways. A longer term lowers the monthly payment but increases total interest, because you are borrowing the money for longer; a shorter term does the reverse, costing more each month but far less overall. Even one percentage point on the rate can shift both the monthly figure and the lifetime interest substantially.
The loan amount scales the payment almost proportionally, which is why a bigger deposit helps twice over: it cuts the sum you borrow and, on many products, can unlock a lower rate. Nudging each input in turn is the quickest way to see which lever matters most for your situation.
Reading the total interest figure
The headline monthly payment tells you what you can afford now; the total interest tells you what the loan really costs. Two mortgages with similar monthly payments can carry very different total interest if their terms differ, so comparing only the monthly figure can be misleading.
Treat total interest as the price of borrowing. Comparing that price across scenarios — a 20-year versus a 30-year term, or a rate half a point lower — turns an abstract decision into concrete money, which is far easier to weigh than percentages alone.
Using it to weigh overpayments
The calculator does not model ad-hoc overpayments directly, but you can approximate their effect. Shorten the term until the monthly payment matches the higher amount you could realistically pay each month; the reduced total interest that results is roughly what consistent overpayments would save you.
This works because overpaying and choosing a shorter term both do the same thing — clear the principal faster so less interest accrues. Bear in mind that some deals cap penalty-free overpayments (often around 10% of the balance a year), so check your product's terms before relying on the saving.
An estimate, not financial advice
This is an educational estimate for a fixed-rate repayment mortgage, not a quote or a recommendation. It assumes the rate holds for the entire term, whereas most fixed deals last two to ten years and then revert to a higher variable rate, so a real long-term cost can differ from the figure shown here.
Your actual offer will depend on fees, your credit history, the loan-to-value ratio, and the specific product, and only a qualified lender or broker can confirm it. Everything is computed in your browser, so no amounts or rates are ever uploaded — use the numbers to plan, then verify them before you commit.
Frequently asked questions
How is the monthly payment calculated?
With the standard amortization formula: M = P × r(1+r)^n / ((1+r)^n − 1), where P is the loan amount, r the monthly rate, and n the number of monthly payments. It is the same math lenders use for repayment mortgages.
Is this financial advice?
No. This is an educational estimate only. Your actual offer depends on fees, your credit history, and the product terms — always confirm figures with a qualified lender or mortgage adviser before committing.
Why does a shorter term cost more per month but less overall?
A shorter term repays the principal faster, so less interest accrues over the life of the loan. The monthly payment rises, but the total interest can fall dramatically — try 20 vs 30 years and compare.
Does the calculator include taxes, insurance, or fees?
No — it estimates principal and interest only. Add property taxes, buildings insurance, and any arrangement fees on top when budgeting.
What happens if interest rates change?
The estimate assumes the rate stays fixed for the whole term. In reality most fixed deals last 2–10 years and then revert; re-run the calculator with the follow-on rate to stress-test your budget.
Is my financial information private?
Yes. The calculation runs entirely in your browser. No amounts, rates, or any other data are uploaded or stored.
Can I use it for overpayments?
Indirectly. Shorten the term until the monthly figure matches what you can pay each month — the reduced total interest approximates what regular overpayments would save.