About Fairrentcalc
An open-source, mathematically grounded approach to splitting rent between roommates.
Why Fairrentcalc Exists
Splitting rent among roommates is one of the most common sources of conflict in shared housing. Traditional methods — dividing the total rent equally, guessing, or relying on whichever roommate shouts the loudest — ignore the real differences between rooms. A roommate with a private bathroom, a walk-in closet, and oversized windows objectively gets more value than someone in a smaller room with shared facilities. Fairrentcalc was built to solve this problem with math instead of arguments.
How It Works
Fairrentcalc uses a three-part approach to help roommates make fair, informed decisions:
- Rent Split Calculator: Input each roommate's room square footage and toggle which amenities they have — private bathroom, balcony, walk-in closet, large windows. Adjust global weight sliders to set how much each feature is worth. The algorithm divides the base rent proportionally by room size, then adds amenity premiums, producing an exact per-person breakdown with a visual chart and detailed table.
- Screen Calibrator: Using a standard credit card (ID-1 format, 85.6mm wide) placed against your screen, the tool auto-detects your display's pixels per inch (PPI) and true diagonal size. Once calibrated, you can lay a floor plan blueprint directly on your screen and measure room dimensions to scale — eliminating guesswork from the equation.
- Listing Evaluator: Before you commit to a lease, enter the listing rent, apartment square footage, and location tier. The tool compares the price against local market averages and evaluates rent affordability using the 30% rule and the 50/30/20 budgeting framework.
Open Source & Free
Fairrentcalc is completely free to use. There are no accounts, no logins, no subscriptions, and no hidden fees. The project is open source, which means the code is publicly available for review, contribution, and verification. Transparency is core to the project — both in how calculations work and in how the software itself is built.
Built with Modern Technology
Fairrentcalc is built with Astro, a static site generator that produces instant-loading multi-page applications. The site uses Tailwind CSS v4 for styling and follows Vercel's design language for a clean, professional interface. The static MPA architecture means every page loads instantly and is fully crawlable by search engines — ensuring the tool is discoverable by anyone searching for a fair way to split rent.
Privacy by Design
All rent calculations, room configurations, and calibration data stay entirely in your browser's local storage. Nothing is ever sent to a server. There are no tracking cookies, no analytics fingerprinting, and no personal data collection. Your rent data is yours alone.
Multi-Language Support
Fairrentcalc supports English, Spanish, French, German, Hindi, and Chinese. The interface adapts to your selected language, and the calculator maintains full functionality across all supported locales.
Get Involved
Fairrentcalc is an ongoing project. If you have suggestions, find a bug, or want to contribute, visit the project's GitHub repository. Feedback and contributions are welcome.