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cannan David
cannan David

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I Built 28 Financial Calculators in 30 Days - Here's What I Learned

#webdev #javascript #productivity #tools

The Problem That Started Everything

Last month, I was helping my sister plan her retirement. We needed multiple calculators - compound interest, retirement planning, tax calculations. Every site we visited was a nightmare:

  • 🚫 Popup ads after every calculation
  • 🚫 Email signup walls
  • 🚫 Broken on mobile
  • 🚫 Suspiciously wrong formulas

So I did what any developer would do - built my own.

What I Built

SuperCalc - 28 professional financial calculators, zero BS.

The Calculator Collection

Investment Tools:

  • Compound Interest Calculator - See your money grow
  • ROI Calculator - Measure investment returns
  • Present Value Calculator - Time value of money

Tax Calculators:

  • Capital Gains Tax - Know your tax liability
  • Estate Tax Calculator - Plan ahead
  • Effective Tax Rate - Your real tax percentage

Business Analysis:

  • Break-Even Calculator - When profit starts
  • EBITDA Calculator - Key business metric
  • Business Valuation - What's it worth?

Personal Finance:

  • Retirement Calculator - Can you retire?
  • Debt-to-Income Ratio - Loan qualification
  • Net Worth Tracker - Track progress

The Tech Stack 

const techStack = {
  framework: 'Next.js 14',
  language: 'TypeScript',
  styling: 'Tailwind CSS',
  hosting: 'Cloudflare Pages',
  cost: '$0/month'
};
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Everything runs client-side for privacy. No backend, no database, no tracking.

Key Lessons Learned

1. People HATE Ads More Than You Think

90% of feedback mentions "thank you for no ads". The ad situation has gotten so bad that a clean interface is now a competitive advantage.

2. Mobile-First Isn't Optional

70% of my users are on mobile. Desktop-first design is dead for consumer tools.

3. Speed > Features

Users prefer 5 fast calculators over 50 slow ones. I cut features ruthlessly to keep load time under 1 second.

4. Trust Through Transparency

Showing the formulas and calculations builds trust. People want to verify the math.

The Results (First Month)

  • 📈 2,500+ unique users
  • ⏱️ 4.5 minute average session
  • 🔄 35% return rate
  • 💬 50+ positive feedback emails
  • 💰 $0 hosting costs

What's Next?

Currently working on:

  • Mortgage calculator with amortization
  • Investment portfolio analyzer
  • Crypto tax calculator
  • API for developers

Try It Yourself

Check it out: https://supercalc.dev

All calculators are free, no signup, no ads. Just clean, accurate financial tools.

Open Source?

Considering open-sourcing the calculation engine. Would anyone be interested? Let me know in the comments.

What calculator tools do you wish existed? Drop a comment - I'm always looking for ideas!

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