American Express Financial Calculators - Auto Loan

I was the lead developer across a suite of about seven interactive financial calculators for American Express Credit Intel, including the Auto Loan Calculator. I built these tools with HTML, CSS, and JavaScript, focusing on fast, responsive UI, accessible form controls, and a consistent interaction pattern so users could quickly understand outcomes without friction across desktop and mobile.

For the Auto Loan Calculator specifically, I implemented the core amortization and payment logic and wired it to a clean input experience with strong validation and guardrails. That included handling common edge cases like zero down payment, short terms, very low or high APRs, and rounding consistency so the monthly payment, total interest, and overall cost stay accurate and stable as users adjust inputs.