Direct answer
Loan amortization is the scheduled repayment of debt through fixed periodic installments, where each installment is split between interest costs and equity principal reduction.
How to use this tool
Enter Loan Principal & Rate
Input total borrowing balance and the nominal annual interest rate.
Set Loan Term & Amortization Method
Select repayment horizon in years and choose between fixed-rate annuity (equal payment) or linear principal (equal principal) models.
Add Optional Prepayments
Enter monthly extra principal amounts to simulate interest savings and early payoff dates.
Inspect Schedule & Export CSV
Review the month-by-month balance trajectory and export the full schedule to a CSV spreadsheet.
How Loan Amortization Works & Mathematical Formula
In equal-payment amortization, the monthly installment P_periodic is calculated from the principal balance L, periodic interest rate r (annual rate divided by 12), and total payment periods n (years multiplied by 12). In early payment periods, interest comprises the bulk of the installment; over time, interest declines and principal reduction accelerates.
- Equal-Payment Amortization maintains constant monthly payments with shifting principal and interest ratios.
- Equal-Principal Amortization starts with higher payments that decrease steadily over time, lowering cumulative interest.
- Extra principal payments reduce the remaining balance immediately, shortening loan duration.
Practical examples
$300,000 30-Year Mortgage at 6.5% Annual Rate
Input: Principal: $300,000, Rate: 6.5%, Term: 30 years (360 months), Extra Payment: $0
Output: Monthly Payment: $1,896.20, Total Interest Paid: $382,633.47, Total Cost: $682,633.47
Under standard 30-year fixed amortization, cumulative interest exceeds original principal without extra prepayments.
Limitations
- Does not include variable escrow fees, property taxes, homeowner insurance, or PMI charges.
- Assumes a fixed interest rate over the full life of the loan without rate reset events.
Frequently asked questions
What happens when I make extra principal payments?
Extra payments directly diminish the outstanding principal balance. Because monthly interest is computed on the current balance, future interest accrual drops, resulting in substantial cumulative interest savings and earlier loan retirement.
Does this tool upload my financial information?
No. FreeKitX processes all financial math directly within your browser runtime. No financial figures or calculations are sent to external infrastructure.
Authoritative References & Standards
- CFPB Consumer Tools: Mortgages and Amortization ↗ — Official guidance on mortgage amortization structures, periodic interest, and debt reduction.