Interest Rate Calculator · Practical guide
How Much Total Interest Will I Pay on My Loan?
Total interest is every dollar you pay beyond what you borrowed — and it's easy to compute.
At a glance
The Quick Formula
Total interest = (monthly payment × number of months) − loan amount. For a $20,000 loan at $377 a month for 5 years: $377 × 60 = $22,620, minus $20,000, equals $2,620 in interest. The calculator above shows this automatically alongside the implied rate and total cost.
Interactive tool
Interest Rate Calculator
Enter your own values, then compare the result with the examples below.
Results
Why the Same Loan Can Cost Very Different Amounts
Interest grows with both the rate and the term. Compare $20,000 loans over 5 years:
| Monthly Payment | Implied Rate | Total Interest |
|---|---|---|
| $377 | 4.95% | $2,620 |
| $400 | 7.42% | $4,000 |
| $450 | 12.50% | $7,000 |
And term matters just as much: $25,000 at $500 a month costs $5,000 in interest over 5 years (7.42%), but $11,000 over 6 years (12.86%) — the longer loan more than doubles the cost for the same monthly outlay.
How Amortization Front-Loads Interest
Early payments are mostly interest because the balance is highest at the start. On a 30-year, $300,000 loan at 6%, the first payment of $1,798.65 sends $1,500 to interest and only $298.65 to principal. By the final years the split reverses. This is why extra principal payments early in a loan save disproportionately more interest than the same payments made later.
Ways to Pay Less
- Shop the rate — solving your quoted payment with the calculator above tells you exactly what rate you're being offered.
- Shorten the term — higher payments, but far less total interest.
- Pay extra toward principal — every extra dollar skips all future interest it would have accrued.
- Put more money down — interest is charged only on what you actually borrow.
Frequently Asked Questions
Is total interest the same as total cost?
No. Total cost is principal plus interest — everything you pay. Total interest is only the portion above what you borrowed. A $22,620 total cost on a $20,000 loan means $2,620 of interest.
Does this include fees or insurance?
No. The calculator's total cost reflects principal and interest only. Roll any financed fees into the loan amount you enter to include them.
Why does a longer term cost more interest at the same payment?
Because the balance shrinks more slowly, interest accrues on a larger balance for more months. The implied rate is also higher when the same payment stretches over more months.
How can I estimate interest before I know my payment?
Work in reverse: enter your expected loan amount, a realistic payment for the term, and note the implied rate. If that rate is far above current market rates, the payment you're picturing is too low for that loan.