Paydown is built and maintained by Johan Gallo, a software developer. I built it to answer a question most bank websites make harder than it should be: "exactly how much of this payment goes to interest, and how does that change if I pay a bit more?" Each calculator is built around a real amortization schedule, not a rough estimate.
Every calculator runs the standard loan amortization formula month by month — the same math a bank uses internally — not a simplified approximation. The mortgage calculator includes PMI rules under the Homeowners Protection Act, the auto loan calculator follows how most states tax trade-ins, and the credit card calculator models the minimum-payment trap exactly as issuers calculate it. Every formula is shown in full on its calculator page, with sources cited at the bottom of each article.
It's not financial advice. These are estimates for planning purposes — actual rates, taxes, fees, and terms depend on your lender, state, and credit profile. Confirm the real numbers with your lender or a licensed financial professional before you sign anything.
This site is free and has no paywall, account, or newsletter. It's supported by display ads and affiliate links (clearly marked) on relevant financial products. Neither one changes what the calculators tell you.
Found a formula that looks wrong, or have a calculator you wish existed? See the contact page.