Monthly Interest Formula
Each month, interest is charged on your remaining balance. Your payment first covers this charge, and the remainder reduces your principal. Extra payments bypass interest entirely and go 100% to principal, reducing the base on which all future interest is calculated.
Variables
- BCurrent BalanceRemaining amount owed
- APRAnnual RateDivided by 12 for monthly rate
- PMonthly PaymentRegular + extra combined
Multi-Debt Strategies
analytics Debt Avalanche
Prioritizes debts with the highest interest rates first. Once the highest-rate debt is paid, its payment (plus your extra cash) rolls over to the next highest. This is mathematically the fastest way to become debt-free and saves the most money.
bolt Debt Snowball
Prioritizes debts with the smallest balances first, regardless of interest rates. Paying off small debts quickly provides immediate psychological "wins," helping you stay motivated. Once a small debt is gone, its full payment rolls into the next one.
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Abdullah Mostafa
Software engineer and creator of FinanceTact. Designs client-side financial tools to make complex amortization formulas transparent and easy to use.
About the creator arrow_forwardCFPB & Federal Reserve Benchmarked
Amortization equations and Snowball/Avalanche payment allocation algorithms are benchmarked against official Consumer Financial Protection Bureau (CFPB) Regulation Z standards and Federal Reserve G.19 credit calculation methods.
Last verified: August 2026*Disclaimer: This tool is for educational and estimating purposes only. It does not constitute financial, accounting, or tax advice. Actual payoff timelines and interest savings will vary based on your specific loan terms and lender policies.