Debt Repayment Simulator

This utility simulates and compares two common strategies for eliminating multiple streams of debt: the Snowball method and the Avalanche method. It is designed for individuals managing various liabilities such as credit cards, student loans, or personal loans who want to understand the mathematical impact of extra payments. Users start by entering a list of their current debts, specifying the outstanding principal balance, annual percentage rate, and minimum required monthly payment for each. Finally, you input any extra discretionary funds you can commit each month across the entire portfolio.

Once you initiate the calculation, the client-side JavaScript engine executes a month-by-month amortization loop for both strategies simultaneously. For the Snowball method, the algorithm sorts your active liabilities by the smallest principal balance and aggressively routes all extra capital and freed-up minimum payments there first. Conversely, the Avalanche simulation sorts your profile strictly by the highest interest rate to mathematically minimize total capital lost to interest. The script tracks the exact month each individual loan zeroes out and aggregates the total interest accrued over the lifespan of the repayment phase, outputting a side-by-side comparison.

Because this simulator operates entirely in your browser environment without external financial APIs, it relies on several fixed assumptions that may not perfectly mirror real-world lender behavior. The mathematical loop calculates interest identically across all inputs using standard monthly compounding based on the provided annual rate, ignoring daily average balance calculations or unique grace periods utilized by specific credit card issuers. Furthermore, the simulation assumes static interest rates, meaning it cannot account for variable-rate loans or expiring promotional zero-percent interest periods. It also assumes you never miss a payment and consistently apply the exact extra amount entered.