When I started building CalculaCentro, I had one goal: create a clean, fast, free calculator site in Portuguese that actually works on mobile.
Most calculator sites I found were either in English, full of ads, or broken on phones. Brazilian and Portuguese users deserved better.
What We Built
Over the past months, we've shipped 100+ calculators across categories:
- Finance: compound interest, loan payments, ROI, inflation adjustment
- Taxes: Brazilian IR, INSS, FGTS, MEI, Simples Nacional
- Health: BMI, BMR, calorie needs, ideal weight
- Math: fractions, percentages, rule of three, equations
- Converters: currency, units, temperature
Key Technical Decisions
No frameworks for calculators – Each calculator is a standalone HTML/JS module. This keeps load times under 1s even on 3G.
Progressive enhancement – Works without JavaScript for basic inputs, enhanced with JS for real-time results.
Mobile-first – 70%+ of our users are on phones. Every layout was designed at 375px width first.
What I Learned
- Portuguese SEO is underserved – There's far less competition for Portuguese calculator keywords than English equivalents.
- Users want explanations – The most-visited pages explain how the calculation works, not just the result.
- Speed matters more than features – A fast, simple calculator beats a slow, feature-rich one every time.
Try It
Check out CalculaCentro – fully free, no signup required.
Would love feedback from the dev community on UX, performance, or anything else!
Top comments (1)
Hey, wanted to share a quick update on CalculaCentro since I last posted about it!
A lot has happened over the past few weeks:
Expanded tool library — We went from 102 to 114 calculation tools across 10 categories. New additions include tools for menstrual cycle tracking, macro nutrients, MEI (solo entrepreneur) taxes, Price/SAC loan table comparison, construction cost estimator, QR code generator, and more.
Full blog system — Added 20 long-form articles (in Portuguese) covering personal finance, Brazilian labor law, health, and everyday math. Each post links to the relevant calculation tools, which has been great for internal linking.
SEO overhaul — Every tool page now has structured data (FAQ schema, BreadcrumbList, Article), dynamic sitemaps (/sitemap.xml, /sitemap-tools.xml, /sitemap-blog.xml), hreflang tags for pt-BR/pt-PT targeting, and 6 hand-written Q&A sections per tool for GEO (Generative Engine Optimization).
Tool rating system — Users can now rate each tool 1–5 stars. Session-based, no login required.
Admin panel sync workflow — Built a two-way database sync system between dev and production environments, fully controlled from the admin panel. This was one of the more interesting engineering challenges — two separate PostgreSQL instances (Replit managed + Neon), dynamic column detection, and JSONB type handling.
Still a lot to do on the SEO front, but Search Console is starting to pick up impressions. Happy to answer any questions! #portuguese #brazil