About Calculy

Our Mission

Calculy.org provides free, accurate, and easy-to-use calculators for everyone. We believe that making informed financial and practical decisions shouldn't require expensive software or professional consultations for basic calculations.

Our goal is simple: give people the same calculation tools that financial professionals use — but make them free, private, and accessible from any device, in any of our supported languages.

Who Built Calculy

Calculy is built and maintained by a small, independent team of software developers and financial mathematics enthusiasts based in Europe. We combine hands-on experience in software engineering, web development, and quantitative analysis to build calculators that are both technically sound and genuinely useful.

We are not a large corporation or a VC-funded startup. Calculy is an independently operated project, which means we answer to our users — not investors. Every design decision is driven by one question: "Does this make the calculator more accurate, faster, or easier to use?"

Our team has professional experience in:

  • Software engineering: Building reliable, well-tested web applications used by thousands of people daily
  • Financial mathematics: Implementing standard formulas used in banking, lending, and investment analysis (amortization, NPV, IRR, compound interest, annuity equations)
  • Energy systems: Modeling solar ROI, heat pump efficiency (COP curves), insulation R/U-values, and long-term energy cost projections
  • Multilingual content: Localizing calculators for 5 markets with country-specific defaults, tax rates, and terminology — not machine-translated, but adapted for each locale

What We Offer

We offer 48+ calculators across multiple categories:

  • Financial Calculators: Loans, mortgages, ROI, compound interest, salary, and more
  • Energy Calculators: Solar panels, heat pumps, home energy costs, insulation savings
  • Auto Calculators: Car costs, fuel vs electric, lease vs buy comparisons
  • Utility Calculators: Percentages, VAT, discounts, unit conversions
  • Date & Life Calculators: Age, dates, pace, relocation costs

All calculators are available in 5 languages: English, German, French, Spanish, and Polish.

Over 30 of our calculators are PRO-grade, featuring interactive Chart.js visualizations, scenario comparisons, sensitivity analysis, CSV export, and detailed amortization or projection schedules. These advanced features are completely free — no paywalls, no "unlock with account" gates.

How We're Different

  • No signup required: Use any calculator instantly
  • No data collection: All calculations happen in your browser
  • Privacy-first: We don't store your inputs or results
  • Always free: No paywalls, no premium features
  • Fast and simple: Clean interface, instant results
  • Independently operated: No corporate agenda, no affiliate bias — we don't sell financial products or earn commissions on recommendations

Technical Details

Calculy.org is a static website built with modern web technologies. All calculations are performed client-side using JavaScript, meaning:

  • Your data never leaves your device
  • The site loads fast and works offline
  • No server-side processing or databases

The site is built with Astro (a modern static site generator), vanilla JavaScript for calculation logic, and Chart.js for interactive data visualizations. We deliberately avoid heavy frontend frameworks to keep page loads fast and the codebase maintainable for the long term.

Our Calculation Methodology

Every calculator on Calculy.org is built with a focus on accuracy, transparency, and practical usefulness. Our development process includes:

  • Standard formulas: All financial calculators use established mathematical formulas — annuity equations, compound interest, NPV/IRR, amortization schedules — the same methods used by banks and financial institutions.
  • Transparent methodology: Each calculator includes a "How it works" section that explains the underlying formula and logic. You can verify every result step by step.
  • Real-world defaults: Default values are based on current market conditions in each country — interest rates, tax rates, energy prices — so results are immediately relevant to your situation.
  • Client-side calculations: All computation happens in your browser. This means your financial data is never transmitted to any server, providing complete privacy by design.

We regularly review and update our calculators to reflect changes in tax rates, interest rates, and regulatory requirements across all supported markets.

Financial Calculator Formulas

Our financial calculators implement well-documented formulas from standard financial mathematics textbooks:

  • Loan & Mortgage: Standard annuity formula PMT = P × r(1+r)^n / ((1+r)^n − 1), with support for both annuity (equal payments) and decreasing (linear) repayment methods. Full month-by-month amortization schedules show principal vs. interest breakdown.
  • Compound Interest: A = P(1 + r/n)^(nt) with configurable compounding frequencies (monthly, quarterly, annually) and optional regular contributions.
  • NPV & IRR: Net Present Value uses standard discounted cashflow summation. Internal Rate of Return is solved iteratively using the Newton-Raphson method.
  • Inflation adjustment: Fisher equation for real vs. nominal returns, purchasing power calculations using CPI-based methodology.

Energy Calculator Models

Energy calculators use established engineering models and publicly available data:

  • Solar ROI: Based on panel wattage, local irradiance estimates, degradation rates (typically 0.5%/year), and current electricity prices per market.
  • Heat Pump: COP (Coefficient of Performance) curves modeled across temperature ranges, compared against gas/oil boiler efficiency ratings.
  • Insulation: R-value and U-value calculations per material type, with energy savings derived from degree-day methodology.

Testing & Verification

Our calculators are verified through multiple methods:

  • Automated E2E tests: We maintain a comprehensive suite of end-to-end tests (using Playwright) that verify calculator outputs against known correct values. These tests run on every code change.
  • Cross-reference: Results are compared against established financial calculators, bank amortization tools, and textbook examples during development.
  • Edge case handling: Calculators are tested with boundary values (zero inputs, very large numbers, unusual combinations) to ensure they handle all scenarios gracefully.
  • User feedback loop: Reported calculation errors are investigated and corrected with the highest priority. Every correction is covered by a new automated test to prevent regression.

Accuracy and Transparency

Calculy.org calculators are built on standard financial and mathematical principles. We use the same formulas that underpin professional financial software: time value of money calculations, standard amortization methods, and established economic models.

For energy calculators, we use typical efficiency values, manufacturer specifications, and publicly available energy price data. All assumptions are clearly stated on each calculator page so you can adjust them to match your specific conditions.

Our calculators provide detailed breakdowns — not just final numbers. When you calculate a loan payment, you see the full amortization schedule. When you compare energy options, you see year-by-year projections. This transparency lets you understand exactly how each result is derived.

Editorial Independence

Calculy.org is an independent project. We do not sell financial products, insurance, or loans. We do not earn referral commissions or affiliate fees from banks, lenders, or energy companies. Our calculators have no hidden bias toward any product or provider.

The site is monetized through display advertising only. Advertising does not influence calculator results, default values, or the content of our educational sections. You will never see a calculator on Calculy that steers you toward a specific financial product.

Disclaimer

The calculators on Calculy.org are provided for informational and educational purposes only. Results are estimates based on the values you enter and the standard formulas described on each page.

Our calculators do not constitute financial, tax, legal, or professional advice. For significant financial decisions — such as taking out a mortgage, investing, or major purchases — we strongly recommend consulting a qualified financial advisor, tax professional, or other relevant specialist who can consider your complete personal situation.

Energy calculators use typical performance values and average energy prices. Actual results will vary depending on your local climate, energy provider, installation quality, and building characteristics. Always obtain professional quotes before making energy-related investments.

Data & Privacy

Your privacy is fundamental to how Calculy.org works — it is built into the architecture, not added as an afterthought:

  • No backend server: Calculy has no application server, no database, and no user accounts. It is a fully static website. All calculations are performed entirely in your browser using JavaScript. Your inputs and results are never sent to or stored on any server.
  • No account required: You can use every calculator without registration, login, or providing any personal information.
  • No tracking of calculations: We do not record what you calculate, what values you enter, or what results you receive. There is no server to send this data to.
  • Local storage only: Some PRO calculators offer an optional "save" feature that uses your browser's local storage. This data stays on your device and can be cleared at any time through your browser settings.
  • No third-party calculation APIs: Your financial data is not sent to any external service for processing. Everything runs locally in your browser tab.

For more details, please see our Privacy Policy.

Contact Us

Have questions, suggestions, or found a bug? We'd love to hear from you:

Email: contact@calculy.org

We welcome feedback on calculator accuracy, feature requests, and suggestions for new calculators. Reports about calculation errors are treated with highest priority.

We typically respond within 1-2 business days. For calculation error reports, please include:

  • Which calculator you used (name and language)
  • The input values you entered
  • The result you received vs. the result you expected
  • A reference source for the expected result (if available)