Simple Mortgage Calculator — Monthly Payment & Total Interest
Find your monthly mortgage repayment, total interest and the principal-vs-interest split. Enter the loan amount, annual interest rate and term — the calculator applies the standard amortisation formula and charts how the balance falls over time.
%
years
Fixed payment each month for the full loan term
607,686.45
Total repaidPrincipal
49.4%
Total interest
50.6%
- 1
Monthly interest rate
6.5 % ÷ 12 ÷ 100 = 0.005417 - 2
Number of payments
25 × 12 = 300 - 3
Growth factor
(1 + 0.005417)ⁿ = 5.0562How much one unit grows over the full term at the monthly rate. - 4
Monthly payment
300,000 × 0.005417 × 5.0562 ÷ (5.0562 − 1) = 2,025.62
How does this calculator work?
Monthly mortgage payment M = P × r(1+r)ⁿ / [(1+r)ⁿ − 1], where r = annual rate / 12 and n = loan months. Total interest = M × n − P. Longer terms reduce monthly payments but dramatically increase total interest. Enter loan amount, rate and term to see your full repayment picture.
Formula
How this is calculated
A fixed-rate mortgage is an amortising loan: each monthly payment covers the interest accrued that month plus a portion of the outstanding principal. Early payments are mostly interest; later payments are mostly principal. The standard amortisation formula M = P × r(1+r)ⁿ / [(1+r)ⁿ − 1] gives the constant monthly amount where P is the loan principal, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of payments.
Total interest = M × n − P. This figure is often large relative to the loan amount: at a 6.5% rate over 25 years, total interest exceeds 75% of the original loan. Making extra payments reduces the outstanding principal faster, shortening the term and saving significant interest — but this calculator assumes the standard schedule with no overpayments.
The calculator uses the nominal (not effective) annual rate divided by 12, which matches how most lenders quote fixed-rate mortgages. Rates and rules vary by country and lender; always verify with your mortgage provider. Other costs — property tax, homeowners insurance, HOA fees, and origination fees — are not included in this estimate.
Frequently asked questions
Extra payments reduce the outstanding principal directly, which lowers future interest charges and can shorten the loan term significantly. For example, one additional monthly payment per year on a 25-year mortgage can cut the term by around 3–4 years depending on the rate. Use an amortisation schedule tool to model specific overpayment scenarios.
This calculator assumes a fixed interest rate for the full term. For an ARM (adjustable-rate mortgage), the payment changes when the rate resets. You can use this tool as a snapshot for each rate period by re-entering the outstanding balance and remaining term at the new rate.
Spreading payments over more months reduces each instalment, but the loan is outstanding longer, accumulating more interest. A 30-year mortgage at 6.5% on £300,000 costs roughly £245,000 in interest vs about £170,000 for a 20-year term — an extra £75,000 for the convenience of a lower monthly payment.
Also known as
TG we-Calculate Editorial Team. (2026). Simple Mortgage Calculator — Monthly Payment & Total Interest [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/simple-mortgage-calculator
TG we-Calculate Editorial Team. "Simple Mortgage Calculator — Monthly Payment & Total Interest." TG we-Calculate. 2026. https://we-calculate.com/calculator/simple-mortgage-calculator.
TG we-Calculate Editorial Team, "Simple Mortgage Calculator — Monthly Payment & Total Interest," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/simple-mortgage-calculator
@misc{wecalculate_simple_mortgage_calculator, title = {Simple Mortgage Calculator — Monthly Payment & Total Interest}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/simple-mortgage-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?