Loan Amortization Schedule Calculator
Free online loan amortization schedule calculator. Generate complete monthly and annual principal and interest payment breakdown tables with extra payoff modeling and Excel export.
Interactive WebAssembly Calculation Engine
This tool runs 100% in your local web browser tab. All amortization schedules, debt yield calculations, and tax deferral projections are computed client-side in WebAssembly. Zero bytes are uploaded to remote servers.
Use the interactive form above to adjust parameters, toggle extra principal schedules, stress-test interest rates, and export full reports to Excel (.xlsx) or CSV.
Underwriting Methodology & Mathematical Formulation
Our calculation algorithms strictly adhere to institutional lending conventions, CFPB disclosure rules, and statutory IRS definitions:
- Standard Annuity Formula: Monthly payment M = P * [r(1+r)^n] / [(1+r)^n - 1], calculating exact interest and principal allocations down to the penny.
- Zero-Roundoff Double Precision: Computations execute using standard IEEE 754 floating-point and integer math to match commercial bank loan documents.
- Sensitivity Analysis: Real-time stress testing against interest rate fluctuations, vacancy rate increases, and balloon maturity horizons.
Frequently Asked Questions
What is an amortization schedule and how does it work?
An amortization schedule is a complete table showing every periodic payment over the life of a loan. Each payment is split between the interest charged by the lender and the principal reduction applied to your loan balance.
How does making extra principal payments affect my amortization table?
Extra principal payments reduce your remaining loan balance immediately. Because subsequent interest charges are calculated on a smaller outstanding balance, more of each future payment goes toward principal, accelerating your debt payoff and saving thousands in lifetime interest.
Why is more interest paid during the early years of a mortgage?
Interest is calculated based on the outstanding principal balance. In the first years of a 30-year mortgage, the balance is at its highest, meaning the interest portion of each fixed payment is large. As the balance decreases over time, the interest portion shrinks while principal repayment grows.