Loan Interest Calculator
Print| Monthly Payment Amount | $0.00 / mo |
| Total Amount Repaid | $0.00 |
The Loan Interest Calculator enables borrowers to compute monthly interest charges, total lifetime interest costs, and total repayment amounts for personal loans, auto loans, mortgages, and business financing. Estimate interest accumulation across simple interest schedules and amortized compounding loans.
The Loan Interest Formula
Interest calculations depend on whether the debt uses simple interest or amortized compound interest:
Simple Interest ($) = Principal × Annual Interest Rate (APR) × Time (Years)
For standard amortized monthly installment loans (mortgages, auto loans, personal loans):
Monthly Payment (PMT) = Principal × [ r(1 + r)^n ] / [ (1 + r)^n - 1 ]
Total Interest Paid = ( Monthly Payment × n ) - Principal
Where:
- Principal: The starting loan amount borrowed.
- r (Monthly Rate): Annual Percentage Rate (APR) divided by 12 months.
- n (Total Months): Scheduled loan repayment term in months.
Total Interest Paid by APR & Term
Compare total lifetime interest charges incurred on a $25,000 principal loan across APR rates and repayment terms:
| Annual APR | 3-Year Term (36 mos) | 5-Year Term (60 mos) | 7-Year Term (84 mos) |
|---|---|---|---|
| 5.00% APR | $1,979.80 Interest | $3,306.20 Interest | $4,675.88 Interest |
| 8.00% APR | $3,205.88 Interest | $5,403.40 Interest | $7,688.12 Interest |
| 12.00% APR | $4,897.28 Interest | $8,367.40 Interest | $12,014.24 Interest |
| 16.00% APR | $6,641.44 Interest | $11,496.20 Interest | $16,680.44 Interest |
Step-by-Step Loan Interest Calculation Example
Here is an example calculating total interest on a $15,000 personal loan at 9.50% APR over a 4-year term (48 months):
- Identify Loan Inputs: Principal = $15,000, APR = 9.50%, Term = 48 months.
- Calculate Monthly Interest Rate:
9.50% / 12 = 0.7917% (0.007917 per month). - Compute Monthly Payment: Applying monthly amortization yields $376.84 per month.
- Calculate Total Repayment Amount:
$376.84 × 48 months = $18,088.32 total paid. - Calculate Total Interest Paid:
$18,088.32 - $15,000 = $3,088.32 total interest cost.
Frequently Asked Questions
What is the difference between simple interest and compound interest on a loan?
Simple interest is calculated strictly on the original principal balance. Compound interest calculates interest on the principal plus previously accumulated unpaid interest.
How does loan term length affect total interest paid?
Shorter loan terms require higher monthly payments but result in drastically lower lifetime interest costs. Longer loan terms lower your monthly bill but significantly increase total interest paid over time.
Can extra payments reduce total loan interest?
Yes. Any additional amount paid directly toward your loan principal immediately reduces the balance on which future interest is calculated, lowering your total lifetime interest.
What is APR and how does it differ from interest rate?
The interest rate is the percentage fee charged to borrow the principal balance. APR (Annual Percentage Rate) incorporates both the base interest rate and mandatory lender fees, showing total annual borrowing cost.