Loan Interest Calculator
Calculate loan interest, total repayment, and monthly payments based on your loan amount, rate, and term.
How This Loan Interest Calculator Works
This calculator determines the total interest cost and monthly payment for a fixed-rate amortizing loan. It uses the standard loan amortization formula, which assumes a constant interest rate and equal monthly payments over the full loan term. The calculation accounts for the declining principal balance, meaning each payment covers the accrued interest first, with the remainder applied to the principal.
The tool provides three key outputs: your monthly payment amount, the total interest paid over the life of the loan, and the total repayment amount (principal plus all interest).
How to Use the Calculator
- Enter the total loan amount you plan to borrow.
- Input the annual interest rate as a percentage (e.g., 6.5 for 6.5%).
- Specify the loan term in years or months.
- Click calculate to see your estimated monthly payment and total interest.
Adjust any input to see how changes in loan size, rate, or term affect your costs.
Understanding Your Results
Monthly Payment: The fixed amount due each month for the entire loan term. This figure includes both principal and interest.
Total Interest: The cumulative interest cost over the full loan period. This is the total cost of borrowing beyond the principal amount.
Total Repayment: The sum of your principal and total interest. This represents the full amount you will pay by the end of the loan term.
These estimates assume on-time payments and no additional fees, prepayments, or changes to the interest rate.
Common Mistakes to Avoid
- Confusing annual rate with monthly rate: The calculator expects an annual percentage rate. Do not divide it by 12 before entering.
- Mismatching term and payment frequency: The calculator assumes monthly payments. If your loan uses a different payment schedule, the results will not be accurate.
- Ignoring additional costs: This calculator covers principal and interest only. It does not include origination fees, closing costs, insurance, or taxes.
Practical Use Cases
- Personal loans: Estimate monthly payments and total interest for debt consolidation or major purchases.
- Auto loans: Compare financing options across different loan amounts, rates, and terms before visiting a dealer.
- Business loans: Evaluate the cost of borrowing for equipment, inventory, or working capital.
- Loan comparison: Test different scenarios to understand how a lower rate or shorter term affects total interest.
Limitations
This calculator assumes a fixed interest rate and a standard amortization schedule. It does not account for:
- Variable or adjustable interest rates
- Balloon payments or interest-only periods
- Prepayment penalties or early payoff scenarios
- Fees, taxes, or insurance included in payments
- Bi-weekly or accelerated payment schedules
For loans with non-standard structures, consult a financial professional or use a more specialized calculator.
FAQ
Does this calculator include fees or insurance?
No. It calculates only principal and interest. Actual loan costs may include origination fees, processing charges, mortgage insurance, or property taxes depending on the loan type.
Can I use this for a mortgage?
Yes, for a fixed-rate mortgage. However, most mortgages include property taxes, homeowners insurance, and possibly PMI in the monthly payment. This calculator does not include those costs.
Why is my monthly payment different from what the lender quoted?
Lenders may include fees, insurance, or other charges in your payment. Differences can also arise from rounding, slight rate variations, or different amortization methods. Use this as an estimate, not a final quote.
What happens if I pay extra each month?
Extra payments reduce the principal faster, which lowers total interest and shortens the loan term. This calculator does not model extra payments, but you can test a shorter term to see the effect.
Is the interest rate compounded monthly?
Yes. The standard amortization formula used here compounds interest monthly, which is the most common method for personal, auto, and mortgage loans.