Loan Interest Calculator
Total interest over the life of any loan.
Total-interest math runs in your browser — zero data leavesYour payment breakdown appears here
Fill in the loan details and press Calculate — the monthly payment, total interest and schedule will render right on this page, with nothing sent to any server.
How to use
The monthly payment hides the real cost of borrowing: the total interest paid over the whole term. This calculator isolates that number so you can compare loan offers and see what a longer term really costs.
How to use
- Enter the loan amount, APR and term in years.
- Press Calculate to see the payment and the lifetime interest.
- Try two terms side by side to feel the difference.
Example
Borrow $20,000 at 6.5% for 5 years: total interest is about $3,479. The same $20,000 at 6.5% for 10 years carries about $7,252 of interest — more than twice as much — even though the monthly payment is much smaller. Time is the silent multiplier.
Formula
Total interest = monthly payment × months − principal. The payment itself comes from the standard PMT formula.
Auto loan angle
Car loans are short, so the interest share is small — on a 5-year car loan interest is often 10-20% of the price. Skipping the longer term keeps it that way.
Student loan angle
Student loans are the extreme case: a 20-year term can push total interest past the original balance. Cutting the term from 20 to 10 years typically halves the interest bill.
Rate vs term, which matters more
Both cut interest, but a shorter term cuts it fastest. Lowering the rate from 7% to 6% on a 5-year, $20,000 loan saves about $560; cutting the term from 6 to 5 years at the same 7% saves about $770.
Add fees to the comparison
Total interest is the pure borrowing cost at the quoted rate. Fees sit on top — run the APR tool when offers include upfront costs, so the comparison between lenders is complete and fair.
FAQ
Why pay attention to total interest?
A low monthly payment on a long term can hide a large interest cost — the total is the true price of borrowing.
Lower the rate or the term?
Both cut interest; a shorter term cuts it fastest.
How much interest on a 5-year car loan?
On a $24,000 loan at 6%, roughly $3,800 over 5 years — about 16% of the amount borrowed.
Can student loan interest exceed the principal?
Yes, on long terms. A 20-year loan at 5% costs about $14,600 of interest on every $20,000 borrowed.
Reviewed by the LoanMath editorial team