Calculator
Total Loan Interest Calculator
Estimate total interest paid over the full term of a fixed-rate amortizing loan. The calculator shows the monthly payment, total paid, and interest cost so you can see the long-term cost of borrowing.
Result
- Total interest
- $7,613.63
- Monthly payment
- $543.56
- Total paid
- $32,613.63
Estimated interest paid across all scheduled payments.
How total loan interest is calculated
The calculator first computes the fixed monthly payment with the standard amortization formula.
It multiplies that monthly payment by the number of payments to estimate total paid over the loan term.
Total interest is total paid minus the original loan amount. This assumes payments are made as scheduled and the rate does not change.
Total loan interest formula
Total Interest = (Monthly Payment x Number of Payments) - PrincipalMonthly payment is calculated from the fixed-rate amortization formula. Total interest then measures the borrowing cost above the principal repaid.
- Monthly Payment is the scheduled principal-and-interest payment.
- Number of Payments is years multiplied by 12.
- Principal is the original loan amount.
What the Numbers Mean
- Loan amount
- The principal borrowed. Larger loan amounts usually increase both payment and total interest.
- Interest rate
- The annual rate used to calculate monthly interest in the amortization formula.
- Loan term
- The repayment length. Longer terms can lower the payment but often increase total interest.
- Total interest
- The amount paid above principal if scheduled payments are made as modeled.
Assumptions
- The loan uses a fixed annual interest rate.
- Payments are monthly and made on schedule.
- No extra payments, skipped payments, late fees, refinance events, or rate changes are included.
- Fees and financed charges are excluded unless already included in the loan amount.
- The result is a planning estimate, not an amortization schedule.
Worked Examples
$25,000 loan at 11% for 5 years
- Input
- $25,000 loan amount, 11% annual rate, 5-year term
- Formula
- $543.56 x 60 - $25,000
- Output
- $7,613.63 total interest
The total paid is about $32,613.63, so interest is the amount above the original principal.
$12,000 loan at 9% for 3 years
- Input
- $12,000 loan amount, 9% annual rate, 3-year term
- Formula
- $381.60 x 36 - $12,000
- Output
- $1,737.48 total interest
A shorter 36-month term limits how long interest accrues.
$35,000 loan at 7.5% for 6 years
- Input
- $35,000 loan amount, 7.5% annual rate, 6-year term
- Formula
- $605.15 x 72 - $35,000
- Output
- $8,571.08 total interest
The lower rate helps, but the 72-month term still creates meaningful lifetime interest.
$15,000 loan at 0% for 5 years
- Input
- $15,000 loan amount, 0% annual rate, 5-year term
- Formula
- $250.00 x 60 - $15,000
- Output
- $0.00 total interest
At 0%, scheduled payments repay principal only.
Same Principal, Different Interest Cost
These examples keep principal fixed where possible so the rate and term tradeoffs are easier to see.
| Example | Rate | Term | Monthly payment | Total interest |
|---|---|---|---|---|
| $20,000 loan | 6% | 3 years | $608.44 | $1,903.79 |
| $20,000 loan | 6% | 5 years | $386.66 | $3,199.36 |
| $20,000 loan | 10% | 5 years | $424.94 | $5,496.45 |
| $20,000 loan | 10% | 7 years | $332.02 | $7,889.99 |
| $25,000 loan | 8% | 3 years | $783.41 | $3,202.73 |
| $25,000 loan | 8% | 6 years | $438.33 | $6,559.83 |
Longer terms can lower monthly payment while increasing total interest.
Lower Payment vs Higher Total Interest
A lower monthly payment can still be more expensive over the full repayment term.
Lower payment, longer term
$20,000 at 10% for 7 years
$332.02/month and $7,889.99 interest
The monthly payment is lower than a 5-year term, but total interest is much higher.
Higher payment, shorter term
$20,000 at 6% for 3 years
$608.44/month and $1,903.79 interest
The payment is higher, but the loan is paid down faster and interest is lower.
Rate pressure
$20,000 for 5 years at 6% vs 10%
$3,199.36 vs $5,496.45 total interest
With the term fixed, a higher rate directly increases lifetime interest.
Related Guides for Interest Cost
Use these when comparing monthly affordability against lifetime borrowing cost.
Frequently Asked Questions
How do I calculate total loan interest?
Calculate the monthly payment, multiply it by the number of payments, then subtract the original loan amount.
Why can total interest be high even when the payment is affordable?
Longer terms spread the loan across more months, which can lower monthly payment while giving interest more time to accrue.
Does this include loan fees?
Only if you include fees in the loan amount. Origination fees, closing costs, and other charges are otherwise excluded.
Does making extra payments change total interest?
Yes. Extra principal payments can reduce the balance faster and lower total interest, but this calculator assumes scheduled payments only.
Is this an amortization schedule?
No. It summarizes payment, total paid, and total interest, but it does not list each monthly balance.
Can I compare different loan terms?
Yes. Run the calculator with different terms and rates to compare monthly payment against lifetime interest.
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Disclaimer
This calculator provides a simplified fixed-rate loan estimate. It is not lending, tax, legal, or financial advice.