Loan Interest Calculator
Calculate the total interest, total repayment and monthly instalment of an equal-monthly-instalment loan.
Input Data
Results
At a glance:The Loan Interest Calculator estimates the total interest cost over the whole term of an equal-monthly-instalment loan (personal loan, private loan, car loan, etc.). It first works out the monthly repayment, then derives total interest as total repayment − loan principal. The longer the term or the higher the rate, the more total interest.
Formula
Monthly rate i = annual rate% ÷ 12; total periods n = term years × 12.
Monthly repayment = loan × i ÷ (1 − (1+i)^−n).
Total repayment = monthly repayment × n.
Total interest = total repayment − loan.
$$i = \\dfrac{\\text{Annual rate}\\%}{12},\\quad n = \\text{Term (years)} \\times 12$$$$\\text{Monthly payment} = \\dfrac{P \\times i}{1 - (1+i)^{-n}}$$$$\\text{Total interest} = \\text{Monthly payment} \\times n - P$$How to Use
- Enter the total loan principal borrowed.
- Enter the annual rate and repayment term.
- View the total interest, total repayment and monthly repayment for the whole term.
FAQ
What does the Loan Interest Calculator actually compute?
It estimates the total interest over the whole term of an equal-monthly-instalment loan (personal loan, private loan, car loan, etc.). It first works out the fixed monthly repayment, then derives total interest as total repayment minus the loan principal.
Why does a longer term cost more interest even if the monthly payment is lower?
Because the principal is outstanding for more periods, so interest accrues for longer. A longer term lowers each monthly payment but raises the total interest paid; a shorter term saves interest at the cost of a higher monthly outlay.
Does the interest rate alone decide the total cost?
The rate is the biggest factor, but the term length and any prepaid fees also matter. Two loans at the same rate can have very different total costs if their terms differ.
What is the difference between total repayment and total interest?
Total repayment is the sum of all monthly instalments over the term (principal plus interest). Total interest is only the interest portion — total repayment minus the original principal.
Are Hong Kong loan rates regulated or capped?
Banks follow the HKMA Code of Banking Practice, while licensed money lenders are subject to the Money Lenders Ordinance (Cap. 163), which caps the effective interest rate. Always check the actual APR and the lender's licence before borrowing.
Related Tools
References
Content review: Calculatorism Finance Team. Results are for reference only; please refer to the relevant authorities for the official figures.