Singapore Car Ownership Calculator

A production-leaning scaffold answering "how much will this car actually cost me to own in Singapore?" — not just the loan instalment.

What's in this build

• Calculation engine (lib/calculations/) — pure, unit-tested functions for loan (flat rate), depreciation, LTA road tax (ICE + EV), fuel, EV charging, parking, insurance (indicative range), tyres, ERP, affordability, total ownership.
• Vitest unit tests for every calculation module (__tests__/calculations.test.ts).
• 6-step wizard at /calculator with live sidebar estimate, breakdown chart, loan-comparison table, assumptions panel, affordability check, and expandable "how is this calculated" details.
• SEO landing pages: /, /calculator, /cars, /cars/[make]/[model], /car-loan-calculator, /road-tax-calculator, /methodology, /data-sources, /privacy, /terms, /contact.
• Sitemap and robots.txt generated by Next.js metadata routes.
• AdSense-ready <AdSlot> component (leaderboard / in-content / sidebar / rectangle); zero actual ad code.
• Seed vehicle catalogue (BMW 320i, Mercedes C180, Toyota, Honda, Tesla Model 3, BYD Atto 3, Prius, Volvo XC40) with OMV/ARF/COE/engine data — clearly marked indicative.
• Seed loan rates (DBS, OCBC, UOB, Maybank, Hong Leong Finance, Tokyo Century) with effective dates.
• Tailwind design system, mobile-first layout, visible focus, chip & card components, WCAG-conscious.

What's not in this build (deliberately)

• No PostgreSQL — seed data lives in /lib/data/*.ts so the app runs on Vercel with zero infra. Swap in a DB when the catalogue grows.
• No SGCarMart URL import — their terms do not permit automated extraction. Manual entry works and the UI surfaces this.
• No admin dashboard — effective dates and sources are embedded in data files; editing is a PR.
• No real LTA/bank/parking live data — all datasets carry effective_date and source and are labelled indicative.
• No account/auth, saved calculations, insurance affiliate, parking search — scaffolding for them is where the data layer would plug in.

Dev

npm install
npm run dev          # http://localhost:3000
npm test             # vitest unit tests
npm run build        # production build

Deploy to Vercel

npx vercel

No env vars required. Optional: NEXT_PUBLIC_SITE_URL for sitemap canonical.

Architecture

app/
  page.tsx                      home
  calculator/                   wizard + state
  cars/[make]/[model]/          per-vehicle SEO pages
  car-loan-calculator/          loan tool
  road-tax-calculator/          road tax tool
  (legal pages, sitemap, robots)
components/                     Field, Breakdown, ResultHero, LoanCompare, AdSlot, …
lib/
  calculations/                 pure engine (one file per cost category)
  data/                         vehicles, loans, fuel prices
  format.ts                     SGD / number formatters
__tests__/                      vitest suite

Every calculation is independently testable; the UI never does maths.

Status vs the spec

Full build order follows the 62-section brief; this is v0 — the shippable core. The scaffolding is where every follow-up (DB, admin, parking search, EV route calculator, ERP route lookup, scenario compare, break-even vs public transport) plugs in cleanly.