Common questions about UK mortgages and repayment calculations.
Your monthly mortgage repayment is calculated using three factors: the loan amount (principal), the interest rate, and the loan term. The formula used is: M = P[r(1+r)^n]/[(1+r)^n-1], where P is the principal, r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments. This ensures equal monthly payments throughout the mortgage term.
With a capital repayment mortgage, each monthly payment reduces both the interest and the outstanding loan balance. By the end of the term you own the property outright. With an interest-only mortgage, your monthly payments only cover the interest — the original loan balance remains unchanged and must be repaid in full at the end of the term via savings, investments or selling the property.
Most UK lenders will lend between 4 and 4.5 times your annual income. Some lenders offer up to 5 or 5.5 times income for higher earners or first-time buyers. For joint applications, lenders typically use a multiple of combined income. Affordability checks also consider your existing debts, monthly outgoings, and a stress test at higher interest rates.
An amortization schedule shows your full mortgage repayment plan month by month. It shows how much of each payment goes toward interest versus reducing the capital balance. In the early years of a mortgage, most of your payment covers interest. Over time, as the balance reduces, more of each payment goes toward the capital.
Overpaying your mortgage reduces your outstanding balance faster, which means you pay less interest overall and can pay off your mortgage earlier. Even small regular overpayments can save thousands of pounds over the mortgage term. For example, overpaying £200/month on a £200,000 25-year mortgage at 4.5% could save over £20,000 in interest and cut 4+ years off the term.
LTV is the ratio of your mortgage loan to the value of the property, expressed as a percentage. For example, if you buy a £300,000 property with a £60,000 deposit, your mortgage is £240,000 — an LTV of 80%. A lower LTV generally means access to better (lower) interest rates. Most lenders require a minimum 5-10% deposit (90-95% LTV max).
When your fixed-rate deal ends, your mortgage typically reverts to the lender's Standard Variable Rate (SVR), which is usually higher. Most borrowers remortgage to a new deal before this happens to avoid the SVR. You can start looking for a new deal up to 6 months before your current deal ends.
For most homeowners, a repayment mortgage is the safer choice because you are guaranteed to own the property outright at the end of the term. Interest-only mortgages are mainly suitable for buy-to-let landlords or borrowers with a clear, reliable repayment vehicle (such as investments or a pension lump sum). Most residential lenders now require a repayment mortgage for owner-occupied properties.
Disclaimer: This calculator is for illustrative purposes only and does not constitute financial advice.
Actual mortgage repayments will depend on your lender, specific product terms, and any fees. Interest rates change frequently.
Always get a personalised quote from a qualified mortgage adviser or lender before making financial decisions.