FutureCalc — Smart & Secure Calculator

A modern, open-source calculator for building wealth safely - security‑first, transparent, and client‑only.

Live Demo: FutureCalc.io Report Card: Open SSF Report Card

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What is FutureCalc?

FutureCalc is a lightweight, privacy‑respecting tool that helps you:

• Split each paycheck between savings and investing
• Build a 6‑month emergency fund
• Understand compounding with clear visuals
• Explore debt payoff, mortgages, and DCA for crypto

Everything runs locally in your browser. No tracking. No backend. Open source.

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Features

Core

• Paycheck planner with percentage sliders and direct input
• Emergency fund target and progress bar (6× monthly expenses by default)
• Growth projection with Investing vs Savings chart
• Contributions vs growth breakdown and time‑based milestones
• Dark mode, responsive UI, accessible colors and keyboard navigation

Calculators

• Debt payoff
  • Avalanche and Snowball strategies
  • Amortization with extra payments
  • Time to payoff, interest saved
  • Balance‑over‑time chart and CSV export
• Mortgage
  • Payment calculation and full amortization
  • Extra payments and time‑to‑payoff
  • 80% LTV milestone estimate (PMI proxy)
  • Balance‑over‑time chart and CSV export
• Crypto (DCA)
  • Periodic buys with fee input
  • Average cost, ending value, max drawdown
  • Portfolio value vs contributions chart and CSV export

Privacy & Performance

• 100% client‑side, no data collection
• LocalStorage for convenience
• No frameworks required, fast load over a CDN

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Why FutureCalc?

Most online calculators are either black boxes or trade convenience for privacy. FutureCalc is:

• Open‑source and auditable
• Explicit about formulas and assumptions
• Built with secure engineering practices from the start

Educational tool only — not financial advice. Returns are hypothetical.

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Security Engineering Focus

Showcasing secure‑by‑default front‑end practices:

• Client‑only architecture
  • No cookies, no sessions, no tracking
  • Inputs persist only in LocalStorage
• Secure coding standards
  • No unsafe eval
  • Scoped functions and listeners
  • Defensive parsing and bounds checking on user inputs
• Supply chain hygiene
  • Dependabot for updates
  • CodeQL for static analysis
  • Linting and formatting in CI
  • OpenSSF Report Card
• Repo hygiene
  • MIT License
  • SECURITY.md for vulnerability reporting
  • Minimal, auditable third‑party usage (Chart.js via CDN)

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Architecture

• Single‑page app: index.html with vanilla HTML/CSS/JS
• ES‑module style organization within one script
• Charts via Chart.js
• No build step; GitHub Pages ready

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Getting Started

Local

• Clone the repo
• Open index.html in a modern browser

GitHub Pages (https://mrguato.github.io/futurecalc/)

• Open Browser for Browser Based Calculator

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Methods and Assumptions (Finance)

• Compound growth: future value with periodic contributions
• Savings APY and investment return applied per‑period
• Debt payoff:
  • Monthly interest accrual, minimums first
  • Extra payment allocated per chosen strategy
• Mortgage:
  • Standard amortization M = P·i·(1+i)^n / ((1+i)^n − 1)
  • Extra payments reduce principal, shortening term
  • 80% LTV milestone as a PMI proxy (informational only)
• Crypto DCA:
  • Units from contribution net of fee
  • Average cost, ending value, max drawdown
  • Optional simulated path for illustration

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Roadmap

• Add UI Changes for Dark & Light Modes
• Add Debt Calculator
• Add Crypto Calculator
• Add Mortgage Calculator
• Add Graphs
• Scenario comparison (e.g., 10% vs 15% investing)
• Real vs nominal returns (inflation toggle)
• FAQ and “Methods” page with citations
• Printable reports for projections and schedules

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Security Policy

See SECURITY.md for how to report a vulnerability.

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License

MIT License © 2025 Jonathan DeLeon

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Contributing

Contributions are welcome. Please open an issue or submit a pull request with clear scope and validation steps.