Money Calculators
Use this loan interest calculator to estimate how much interest a loan may cost over time and how extra payments can reduce it.
Quick answer
Loan Interest Calculator calculates total loan interest from loan amount, interest rate and term years. The core method is Monthly interest = remaining balance x annual rate / 12; total interest = sum of monthly interest charges.
Live calculator
Estimated over 60 monthly payments.
$405.53 required payment plus extra payment.
Principal plus estimated interest.
Compared with making only the scheduled payment.
This estimate uses an amortized monthly payment. Each payment first covers accrued interest, then reduces principal. Extra payments reduce principal faster and can cut interest over the life of the loan.
Quick view of the payment schedule and interest cost.
| Measure | Estimate |
|---|---|
| Loan amount | $20,000.00 |
| Scheduled term | 60 months |
| Payoff time | 60 months |
| Total interest | $4,331.67 |
| Total paid | $24,331.67 |
Annual principal, interest, and remaining balance.
| Year | Principal | Interest | Ending balance |
|---|---|---|---|
| Year 1 | $3,388.80 | $1,477.53 | $16,611.20 |
| Year 2 | $3,670.07 | $1,196.26 | $12,941.13 |
| Year 3 | $3,974.69 | $891.65 | $8,966.44 |
| Year 4 | $4,304.58 | $561.75 | $4,661.86 |
| Year 5 | $4,661.86 | $204.47 | $0.00 |
Formula
Monthly interest = remaining balance x annual rate / 12; total interest = sum of monthly interest chargesThe calculator uses an amortized monthly payment, then adds each month's interest until the loan is paid off.
How to use
Example
Calculator use
Before relying on it
Details
These notes make the assumptions explicit, especially where the same search query can mean slightly different things.
Early payments usually carry more interest because the remaining balance is larger. Later payments shift more toward principal.
Extra principal payments can reduce the balance faster, which can reduce future interest if the lender applies them to principal.
This estimate does not include origination fees, late fees, taxes, insurance, or other charges unless you add them to the loan amount.
Source notes
Benchmarks
The calculator is a decision aid, not a fixed rule. Use the output to compare scenarios and document your assumptions.
Shorter terms usually cost less interest but require higher monthly payments.
Longer terms can lower the payment but usually increase total interest.
Even small extra payments can reduce interest when they consistently lower principal.
Calculator accuracy
The formula, inputs, example, and limitations are shown so the result is checkable, not just a number in a box.
Monthly interest = remaining balance x annual rate / 12; total interest = sum of monthly interest charges
Loan amount, Interest rate, Term years, Extra payment
Results are estimates for quick planning and should be checked before important financial, legal, tax, health, or business decisions.
May 25, 2026
Toolkit Shelf. Loan Interest Calculator. Retrieved May 25, 2026, from https://toolkitshelf.com/tools/loan-interest-calculator
FAQ
For an amortized loan, each month multiplies the remaining balance by the monthly interest rate, then the rest of the payment reduces principal.
Interest is based on the remaining balance. The balance is largest early, so the interest portion is usually larger early.
They can if the lender applies them to principal. Lower principal means less future interest accrues.