Interactive explainer
How the Amortization Calculator works
Use this explainer to see how a fixed loan shifts from mostly interest early to mostly principal later.
Live explainer
Adjust the assumptions
Change inputs here to see the same calculation logic update immediately.
Enter the starting principal balance.
Use the annual interest rate for the loan.
Enter the repayment period in years.
Choose the first payment or schedule start date.
Immediate results
Scheduled Monthly Payment
$377.42
Total Interest Paid
$2,645.48
Annual Schedule
Table output
Open the calculator for the full detailed output.
Sensitivity analysis
Term and rate have the largest lifetime-interest effect. Amount mostly scales the payment and interest totals.
| Input | Scenario | Input value | Output | Output value |
|---|---|---|---|---|
| Loan Amount | -10% | $18,000.00 | Scheduled Monthly Payment | $339.68 |
| Loan Amount | Current | $20,000.00 | Scheduled Monthly Payment | $377.42 |
| Loan Amount | +10% | $22,000.00 | Scheduled Monthly Payment | $415.17 |
| Interest Rate | -10% | 4.5% | Scheduled Monthly Payment | $372.86 |
| Interest Rate | Current | 5% | Scheduled Monthly Payment | $377.42 |
| Interest Rate | +10% | 5.5% | Scheduled Monthly Payment | $382.02 |
| Loan Term | -10% | 4.5 Years | Scheduled Monthly Payment | $414.37 |
| Loan Term | Current | 5 Years | Scheduled Monthly Payment | $377.42 |
| Loan Term | +10% | 5.5 Years | Scheduled Monthly Payment | $347.23 |
Formula and calculation model
Each month, the interest is calculated on the *current* balance (Balance * Rate / 12). The rest of your fixed monthly payment goes to reducing the principal. As the balance drops, interest drops, and principal repayment accelerates.
Input definitions
Loan Amount
The initial principal balance of the loan.
Interest Rate
Use the annual interest rate for the loan.
Loan Term
The total lifespan of the loan (e.g., 30 years for a standard mortgage).
Start Date
Choose the first payment or schedule start date.
What the results mean
Scheduled monthly payment
The fixed payment needed to pay off the loan over the term.
Total interest paid
The borrowing cost across the full modeled schedule.
Common mistakes
Expecting balance to fall evenly
Early payments on long loans are interest-heavy.
Use the schedule to inspect interest and principal by year.
Comparing payments without total interest
A longer term can look cheaper month to month while costing more overall.
Compare total interest before choosing a term.
Scenario and industry examples
Scenario
Five-year auto-style loan
Shorter term with faster principal paydown.
Scenario
Thirty-year mortgage-style loan
Longer term with slow early balance reduction.
Residential mortgage
Mortgage review
Compare a 15-year and 30-year schedule to evaluate total interest.
Auto lending
Vehicle financing
Use a five-year schedule to see how quickly balance falls.
Glossary
- Principal
- The amount of money borrowed that must be repaid.
- Interest
- The charge for the privilege of borrowing money.
- Equity
- The portion of the asset you own (Value - Remaining Balance).
FAQ clusters
Amortization basics
Does this include every lender fee?
No. The calculator focuses on the main payment math. Review lender disclosures for origination, documentation, title, prepaid interest, and other fees.
Why compare total interest as well as monthly payment?
A lower monthly payment can hide a higher lifetime cost when the repayment term is longer.