Loan Interest Calculator — Total Interest on a Loan
Find out exactly how much interest you will pay over the life of any amortising loan. Enter the loan amount, the annual interest rate, and the term in months to see the total interest, total payments, and what fraction of your payments is interest versus principal.
%
months
Total cost of borrowing over the full loan term
431,676.38
total paidPrincipal
46.3%
Total interest
53.7%
- 1
Monthly interest rate
r = 6% ÷ 12 ÷ 100 = 0.005 - 2
Monthly payment
200,000 × 0.005 × 6.0226 ÷ (6.0226 − 1) = 1,199.1 - 3
Total of all payments
1,199.1 × 360 = 431,676.38 - 4
Total interest paid
431,676.38 − 200,000 = 231,676.38Total paid minus the original principal gives the pure cost of borrowing.
How does this calculator work?
Monthly payment M = P·r·(1+r)^n / ((1+r)^n − 1). Total interest = M × n − P. For a $200,000 loan at 6% over 30 years, M ≈ $1,199 and total interest ≈ $231,700. Enter your loan details to see the exact cost of borrowing — and the principal vs interest split on the donut chart.
Formula
How this is calculated
An amortising loan is repaid in equal monthly payments M, calculated from the principal P, monthly rate r, and number of payments n using M = P·r·(1+r)^n / ((1+r)^n − 1). Each payment covers the interest accrued on the current balance and reduces the principal by the rest. Summing all payments gives M × n; subtracting the original principal gives the total interest — the true cost of borrowing.
The interest-to-principal ratio and the donut chart show how much of the total repayment is interest versus principal. For a typical 30-year mortgage at 6%, interest can exceed the original loan amount — the calculator makes this cost explicit so you can compare rates and terms with full information.
This calculator assumes a fixed rate and equal monthly payments from day one. Variable-rate loans, balloon payments, origination fees, and mortgage insurance are not modelled. For comprehensive cost comparison use the APR (Annual Percentage Rate) rather than the nominal rate, as APR bundles upfront fees.
Frequently asked questions
For long terms and moderate-to-high rates, interest compounds on the outstanding balance for many years. A $200,000 loan at 6% over 30 years incurs about $231,700 in total interest — more than the principal itself. Shortening the term or increasing payments are the most effective ways to reduce total interest.
This ratio shows how many dollars of interest are paid per dollar of principal borrowed. A ratio of 1.16× means you pay $1.16 in interest for every $1.00 borrowed. The ratio rises sharply with longer terms and higher rates — useful for quick comparisons without doing full calculations.
The most effective levers are: (1) negotiating a lower interest rate, (2) choosing a shorter loan term, and (3) making extra principal payments. Even a small extra monthly payment can shave years off the loan and save thousands in interest because it reduces the balance on which future interest is charged.
TG we-Calculate Editorial Team. (2026). Loan Interest Calculator — Total Interest on a Loan [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/loan-interest-calculator
TG we-Calculate Editorial Team. "Loan Interest Calculator — Total Interest on a Loan." TG we-Calculate. 2026. https://we-calculate.com/calculator/loan-interest-calculator.
TG we-Calculate Editorial Team, "Loan Interest Calculator — Total Interest on a Loan," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/loan-interest-calculator
@misc{wecalculate_loan_interest_calculator, title = {Loan Interest Calculator — Total Interest on a Loan}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/loan-interest-calculator}}, year = {2026}, note = {TG we-Calculate} }
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