How to Add Loan Amortization to Your App in 5 Minutes (No Math Required)

Every finance app eventually needs loan amortization. The math behind it isn't hard, but implementing it correctly — handling rounding, edge cases, irregular payments — takes longer than you'd think. Here's how to skip all that with a single API call. The Setup You'll need a free API key from RapidAPI . Sign up takes 30 seconds — free tier gives you 50 calls/day. The Code async function getAmortizationSchedule ({ principal , annualRate , termMonths }) { const url = new URL ( ' https://fincalcapi.p.rapidapi.com/amortize ' ); url . searchParams . set ( ' principal ' , principal ); url . searchParams . set ( ' annual_rate ' , annualRate ); url . searchParams . set ( ' term_months ' , termMonths ); const response = await fetch ( url , { headers : { ' X-RapidAPI-Key ' : process . env . RAPIDAPI_KEY , ' X-RapidAPI-Host ' : ' fincalcapi.p.rapidapi.com ' , }, }); if ( ! response . ok ) throw new Error ( ' API error: ' + response . status ); return response . json (); } const schedule = await g