Free UK Mortgage Calculators

Fixed vs Variable Rate Calculator

A fixed rate locks your monthly payment for a set period, typically two or five years, giving you certainty regardless of what happens to the Bank of England base rate. A variable or tracker rate can be cheaper at the outset but rises and falls with the market, which means your payments can increase without warning.

This calculator compares the total cost of each deal over the period you choose, so you can see whether the security of a fixed rate is worth the premium, or whether the risk of a variable rate pays off in your scenario. With the Bank of England base rate currently at 3.75% (July 2026), the gap between fixed and tracker products has narrowed, making this comparison more important than ever.

How Does a Mortgage Calculator Work?

A mortgage calculator uses the standard amortisation formula to work out how much you pay each month on a repayment mortgage. It takes your total loan amount, divides it across the number of monthly payments in your term, and adds the interest charged on the outstanding balance each month. In the early years, most of your payment goes towards interest. As the balance shrinks, more of each payment chips away at the capital.

The formula assumes a fixed interest rate for the full term. In reality, most UK borrowers remortgage every two to five years when their fixed deal ends, so the numbers will shift over time. Think of the calculator as a snapshot of your costs under today's rate, not a guarantee of what you will pay over 25 or 30 years.

What Affects Your Monthly Mortgage Payment?

Four things drive what you pay each month: the amount you borrow, the interest rate, the mortgage term, and whether you are on a repayment or interest-only basis. Here is how each one moves the number.

Loan amount. The more you borrow, the higher your payment. A £50,000 increase on a 25-year term at 4.5% adds roughly £278 to the monthly cost.

Interest rate. Even small rate differences add up. On a £250,000 mortgage over 25 years, the difference between 4% and 5% is around £150 a month, or £45,000 over the full term.

Mortgage term. A longer term reduces monthly payments but increases the total interest you pay. Shortening the term does the opposite, higher payments but less interest overall.

Repayment type. A repayment mortgage clears the debt by the end of the term. An interest-only mortgage keeps the balance the same, so payments are lower, but you need a separate plan to repay the capital. The calculators above model repayment mortgages only.

Calculator vs Adviser: When Do You Need More Than Numbers?

A calculator tells you what a mortgage costs. An adviser tells you which mortgage you can actually get, and whether it is the right one. The difference matters when your situation has any complexity, for example if you are self-employed with limited accounts, buying through a limited company, dealing with bad credit, or using family support through a JBSP mortgage.

Calculators also cannot factor in lender fees, cashback offers, early repayment charges, or the specific criteria each lender applies to your income type. A whole-of-market adviser searches across 90+ lenders and shows you the deals the calculator cannot see.

Frequently Asked Questions

How accurate is a mortgage calculator?
Very accurate for estimating monthly repayments, provided you enter realistic figures. It uses the same amortisation formula lenders use. However, it does not include fees, insurance, or lender-specific criteria, so your actual offer may differ slightly.

Can I use a mortgage calculator for buy-to-let?
You can use the repayment calculator to estimate monthly costs, but buy-to-let affordability is assessed differently, lenders focus on rental income covering 125% to 145% of the payment rather than your personal income. For a proper BTL calculation, speak to a buy-to-let specialist.

What interest rate should I enter?
Use the rate from a deal you are considering, or check current average rates. As of July 2026, typical 2-year fixed rates sit in the high 3% to low 4% range, and 5-year fixes are similar. The Bank of England base rate is 3.75%.

Does using a mortgage calculator affect my credit score?
No. A calculator is a maths tool running in your browser. It does not connect to any lender or credit agency and leaves no trace on your credit file.

What is the difference between a repayment and interest-only mortgage?
A repayment mortgage pays off both interest and capital each month, clearing the debt by the end of the term. An interest-only mortgage pays just the interest, so the original loan amount stays the same and must be repaid separately. The calculators on this page model repayment mortgages.

How much can I borrow on a UK mortgage?
Most lenders offer between 4 and 4.5 times your annual household income, though some specialist or professional lenders stretch to 5 or 6 times for stronger profiles. The exact figure depends on your income, deposit, credit history, and existing commitments.

Should I overpay my mortgage or save?
It depends on your mortgage rate versus your savings rate. If your mortgage rate is higher than the after-tax return on savings, overpaying usually wins. Check your lender's overpayment limit first, typically 10% of the balance per year without penalty.