Mortgage Calculator

Calculate Your Mortgage Payments

Per Bank of England analysis, small changes in rate or term can significantly affect both your monthly payment and total cost. This calculator shows you exactly what you'll pay—and helps you understand the trade-offs. To understand how much you can borrow, check our affordability calculator.

Understanding Your Results

The calculator gives you three key figures. Here's what each one actually means for your finances.

Monthly Payment

This is what you'll pay each month throughout the mortgage term (assuming the rate stays constant). For repayment mortgages, this includes both interest and a portion of the loan itself.

Total Repayable

This is the total amount you'll pay over the entire mortgage term: the original loan plus all interest. On a typical mortgage, the interest portion often exceeds £100,000.

Total Interest Paid

This shows how much of your total repayments goes to interest rather than paying down the loan. It's often a sobering number—but understanding it helps you make informed decisions about overpayments and term length.

How We Calculate

The mortgage payment formula uses standard amortisation calculations.

For Repayment Mortgages

The monthly payment is calculated using:

M = P × [r(1+r)^n] / [(1+r)^n – 1]

Where:

• M = Monthly payment
• P = Principal (loan amount)
• r = Monthly interest rate (annual rate ÷ 12)
• n = Total number of payments (years × 12)

For Interest-Only Mortgages

Interest-only is simpler: you pay only the monthly interest.

M = P × (r ÷ 12)

At the end of the term, you still owe the full original loan amount.

Assumptions We Make

This calculator assumes:

• The interest rate stays constant throughout the term
• You make regular monthly payments
• No overpayments or underpayments
• The term runs its full course

According to UK Finance data, in reality, most people remortgage every 2-5 years when fixed terms end, so rates will change. Use this as a guide for your current deal, not a lifetime prediction. Learn more about choosing between 2-year and 5-year fixed mortgages.

Factors That Affect Your Payment

Understanding these variables helps you make better mortgage choices.

Loan Amount

Borrow more, pay more. A £10,000 increase in borrowing at 4.5% over 25 years adds roughly £56 to your monthly payment and £6,700 to total interest.

Interest Rate

Small rate differences compound significantly. Here's the impact:

That 0.5% difference? It's £71 per month and over £21,000 in total interest.

Mortgage Term

Longer terms mean lower monthly payments but significantly more interest overall. Compare different mortgage types to find the best fit for your circumstances.

Extending from 25 to 30 years reduces your payment by £123 per month—but costs an extra £39,000 in interest.

Repayment vs Interest-Only

Interest-only payments are dramatically lower, but you don't reduce the loan.

For £250,000 at 4.5%:

• Repayment (25yr): £1,390/month, £0 owed at end
• Interest-only: £938/month, £250,000 still owed at end

Interest-only requires a separate plan to repay the capital.

What's Not Included

This calculator shows mortgage payments only. Your actual monthly housing costs include more.

Insurance Requirements

Lenders require buildings insurance. Most buyers also want contents insurance. Budget £20-50 per month.

Fees and Charges

Mortgage arrangement fees (£0-2,000), valuation fees (£0-500), and legal fees (£800-1,500) aren't included in the monthly payment but affect your total cost.

Rate Changes

Per Bank of England guidance, after your fixed period ends, you'll move to a new rate—either by remortgaging or falling onto the lender's SVR. This calculator shows one rate; reality involves changes over time.

Overpayments

If you plan to overpay, your actual term will be shorter and total interest will be lower. Most mortgages allow 10% overpayment per year without penalty.

Using This Information

The calculator is a tool for comparison and planning, not a final answer.

Comparing Scenarios

Try different combinations:

• What if you borrowed £20,000 less?
• What's the impact of a 0.25% rate difference?
• How does extending the term by 5 years affect things?

This helps you understand trade-offs and make informed decisions.

Budget Planning

Your mortgage payment is just one part of housing costs. A common guideline is that total housing costs (mortgage, insurance, maintenance) shouldn't exceed 35% of take-home pay.

The honest answer is that what's comfortable varies by individual. Some people happily spend 40%; others feel stretched at 30%. Know your own finances.

Rate Comparison

When comparing mortgage offers, the headline rate isn't everything. A 4.0% rate with £1,500 in fees might cost more than 4.25% with no fees, depending on your loan size and how long you keep the mortgage.

Why is my calculation different from what the lender quoted?

Lenders may include fees in their quoted payment, use slightly different calculation methods, or show APRC (annual percentage rate of charge) which factors in fees. This calculator shows the basic payment based on principal, rate, and term only.

How accurate is this calculator?

For the inputs you provide, it's mathematically precise. However, it assumes constant rates and regular payments. Real mortgages involve rate changes, potential overpayments, and other variables. Use it for comparison and planning, not as a guarantee.

Should I choose a longer term for lower payments?

It depends on your priorities. Longer terms reduce monthly payments but increase total interest significantly. If affordability is tight now but you expect income growth, starting longer and overpaying later can work. If you can comfortably afford shorter-term payments, you'll save substantially on interest.

Next Steps

With a clear picture of your potential payments, you're better equipped to search for properties within budget and compare mortgage offers effectively.