How I built 50+ Korean tax calculators with Next.js SSG

The Problem

Calculating Korean taxes is painful. Severance pay, 4 major insurances (National Pension, Health, Employment, Industrial Accident), income tax brackets — every year the rates change, and most online calculators are outdated or ad-heavy.

The Solution

I built gye-san.com — 50+ free calculators covering everything from net salary to capital gains tax, all updated for 2026.

Tech Stack

• Next.js (Static Site Generation, output: export)
• Cloudflare Pages for hosting (sub-1s load globally)
• Single JSON data file drives all 50+ calculator pages via dynamic [slug].jsx routing

Key Architecture Decisions

Programmatic SEO

Each calculator page is auto-generated from calculators.json with:

• Dynamic meta titles/descriptions
• JSON-LD Schema (WebApplication + FAQ + BreadcrumbList)
• Auto-generated sitemap
• Internal linking between related calculators (same pillar)

PWA Support

Added next-pwa so users can install it as an app on mobile.

Results

• Lighthouse: 90+ across all categories
• 50+ calculator pages indexed
• Zero server costs (Cloudflare Pages free tier)

Open Source

Calculator logic is available at github.com/chapoleon/korean-tax-calc

🔗 Try it live: gye-san.com

Would love any feedback or suggestions!