Loan Calculator

· 1 min read

Bilingual loan calculator with amortization schedules, affordability analysis, and early repayment simulation

github | demo

tags: finance, calculator, bilingual, tools

stack: Next.js 16, React 19, TypeScript, Tailwind CSS, Chart.js

What

A bilingual (EN/VI) loan calculator built with Next.js 16 App Router and React 19. Supports annuity and fixed-principal repayment methods with variable interest rates per year. Deployed as a static-friendly Next.js app.

Why

Needed a transparent tool to compare loan repayment strategies with Vietnamese bank-style variable interest rates. Most online calculators only support a single fixed rate and lack side-by-side method comparison.

Notes

  • Two calculation methods: annuity (PMT formula) and fixed principal with reducing interest
  • Affordability calculator using DTI ratio thresholds (36%/43%)
  • Early repayment simulator showing interest savings
  • URL sharing via pako-compressed base64 query params
  • PDF export with jspdf + autotable; Vietnamese output uses ASCII-safe text due to font limitations
  • Save/load multiple loan plans to localStorage
  • Charts: line (balance over time), bar (interest vs principal), doughnut (payment breakdown)