Amortization Calculator
Print| Total Cumulative Interest Paid | $0.00 |
| Total Overall Payments Made | $0.00 |
Visualize how every dollar of your monthly loan payment is allocated over time. Use this Amortization Calculator to generate full monthly amortization schedules, track principal reduction versus interest charges over 15 to 30 years, and evaluate extra principal payment interest savings.
The Formula for Loan Amortization
Calculating the fixed monthly payment and itemizing monthly principal versus interest portions relies on standard loan amortization formulas:
Monthly Payment (PMT) = P × [r(1 + r)^n] / [(1 + r)^n - 1]
Interest Component (Month m) = Balance_(m-1) × (r / 12)
Principal Component (Month m) = PMT - Interest Component
Where:
- P: Initial loan principal balance.
- r: Annual interest rate (APR).
- n: Total loan term in months (e.g., 360 for 30 years, 180 for 15 years).
- Balance_(m-1): Remaining principal balance at beginning of month m.
Sample Loan Amortization Milestone Schedule Matrix
Refer to the lookup table below for a sample $350,000 30-year fixed mortgage at 6.0% APR, showing how the monthly payment breakdown shifts from interest to principal over time:
| Loan Year / Milestone | Monthly Payment | Monthly Principal Portion | Monthly Interest Portion | Remaining Principal Balance |
|---|---|---|---|---|
| Year 1 (Payment 1) | $2,098 / month | $348 (16.6%) | $1,750 (83.4%) | $349,652 |
| Year 10 (Payment 120) | $2,098 / month | $634 (30.2%) | $1,464 (69.8%) | $292,168 |
| Year 20 (Payment 240) | $2,098 / month | $1,154 (55.0%) | $944 (45.0%) | $187,645 |
| Year 30 (Payment 360) | $2,098 / month | $2,088 (99.5%) | $10 (0.5%) | $0 (Paid Off) |
Step-by-Step Amortization Calculation Example
Consider a $250,000 loan at 6.0% APR over 30 years ($1,498.88 monthly payment):
- Calculate Month 1 Interest Charge: $250,000 × (0.06 / 12) = $1,250.00 interest.
- Calculate Month 1 Principal Reduction: $1,498.88 monthly payment – $1,250.00 interest = $248.88 principal paid.
- Calculate End of Month 1 Balance: $250,000 – $248.88 = $249,751.12 remaining principal balance.
- Calculate Month 2 Interest Charge: $249,751.12 × (0.06 / 12) = $1,248.76 interest (interest drops by $1.24).
- Calculate Month 2 Principal Reduction: $1,498.88 – $1,248.76 = $250.12 principal paid (principal increases by $1.24).
Frequently Asked Questions
Why is a mortgage payment mostly interest during the first few years?
Because interest is calculated based on the remaining principal balance, early payments feature high interest charges because the principal balance is at its highest point.
How do extra principal payments affect my amortization schedule?
Making extra principal payments directly reduces your loan balance, bypassing interest charges. This shortens your overall loan term and saves thousands of dollars in total lifetime interest.
What is the difference between a 15-year and 30-year amortization schedule?
A 15-year amortization schedule has higher monthly payments, but pays off the principal twice as fast and incurs 50% to 65% less total lifetime interest compared to a 30-year schedule.
Can an amortization schedule change on a fixed-rate mortgage?
No, on a fixed-rate mortgage, the monthly principal and interest payment and full amortization schedule remain 100% fixed unless you make extra principal prepayments or refinance the loan.