I spent the last few months building CalculatorFlux, a free calculator platform with 166 tools covering payroll, finance, health, math, and construction. Here is what I learned along the way.
Why Next.js
App Router made it easy to give each calculator its own route, metadata, and JSON-LD schema without any extra config. Static generation meant every page loads fast with no server delay.
All calculators run client-side
Every calculator runs entirely in the browser. No API calls, no server, no database. The user's numbers never leave their device. This was a deliberate privacy decision and it also made hosting much simpler.
50 state paycheck calculators
The hardest part was building paycheck calculators for all 50 US states. Each state has different tax brackets, flat rates, or no income tax at all. I built a shared calculation engine and passed state-specific tax tables as config objects.
SEO at scale
Each calculator page has its own title, meta description, canonical URL, and structured data. Blog posts live at /resources/[slug] and link back to related calculators.
The result
166 free calculators, all 50 US states covered, updated for 2025-26 tax rates.
Check it out at calculatorflux.com. Feedback welcome.
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