Mortgage Calculator
Estimate your monthly payment and see the full year-by-year amortization schedule.
How the mortgage payment is calculated
This calculator uses the standard fixed-rate amortization formula to spread your loan amount — home price minus down payment — evenly across equal monthly payments for the full loan term. Each payment is split between interest, charged on the remaining balance, and principal, which reduces the balance. Early payments are interest-heavy because the balance is still high; later payments are mostly principal as the balance shrinks. The year-by-year schedule below rolls up all twelve monthly payments in each year into a single row.
With this calculator's default inputs — a £400,000 home, £80,000 down payment, 6.5% rate over 30 years — the loan amount is £320,000, giving a loan-to-value of 80%, right at the edge where lenders typically start offering their best rates. Before comparing this payment against your budget, it's worth checking it against a stress-tested rate and your maximum affordable purchase price using the Mortgage Stress Test calculator and the Max Affordable Property calculator, and against local income levels using the House Price to Income calculator.
Frequently asked questions
- What does this calculator include?
- Principal and interest only, using a standard fixed-rate amortization formula. It does not include property tax, homeowners insurance, PMI or HOA fees, which vary by lender and location.
- How is the monthly payment calculated?
- From the loan amount (home price minus down payment), the monthly interest rate, and the number of monthly payments over the loan term, using the standard fixed-rate amortization formula.
- Why does the schedule show yearly figures instead of monthly?
- A 30-year loan has 360 monthly payments — the schedule rolls those up into one row per year, showing the principal and interest paid that year and the remaining balance at year end.
- Why does more of my payment go to interest early in the loan?
- Interest is charged on the remaining balance, which is highest at the start. As the balance shrinks with each payment, less of each payment goes to interest and more goes to principal.
- Can I use this in my own app?
- Yes — every calculator on Stupidly Clever has a matching REST API and MCP tool that runs the same underlying logic.
- What is LTV (loan-to-value) and why does it matter?
- LTV is the mortgage amount as a percentage of the property value. Lenders use it to set your interest rate — lower LTV (larger deposit) gets better rates because the lender has more collateral buffer. Most competitive deals require LTV ≤ 75–80%; above 90% LTV typically means a significant rate premium.
- What is an offset mortgage?
- An offset mortgage links your savings account balance to your mortgage — instead of earning interest on savings, you reduce the mortgage interest charged. If your mortgage is £200k and you have £30k in savings, you only pay interest on £170k. It's particularly effective for higher-rate taxpayers who would otherwise pay tax on savings interest.