American Express Financial Calculators - Debt Consolidation

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I was the lead developer across a suite of about seven interactive financial calculators for American Express Credit Intel, including the credit card debt consolidation calculator, a Credit Intel interactive that helps users compare payoff scenarios and understand tradeoffs like interest cost, monthly payment, and timeline. I built the experience end to end with HTML, CSS, and JavaScript, focusing on a clean UI, responsive layout, and accessibility so it worked smoothly across devices and was usable with keyboards and screen readers.

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The harder part was the math: implementing and validating the financial calculations with careful handling for rounding, input constraints, edge cases, and realistic output formatting that stays consistent as inputs change. I also added guardrails and clear error states to prevent bad inputs, and structured the code to be maintainable as requirements evolved, since these tools tend to get iterative updates once stakeholders see real user behavior.