Public housing calculator boundary

The calculator in assets/housing-calculator.js is a separate public implementation. It does not import from, bundle, or call the private housing_decision package, its defaults, notebooks, Flask routes, SQLite database, saved comparisons, or local server.

Privacy architecture

• Calculation happens in the visitor’s browser.
• Comparisons are stored in that browser’s localStorage under ritvikmath.housing.public.v1.
• New visitors start with no saved comparisons.
• Inputs never appear in a URL and no financial-input API exists.
• JSON and CSV exports are created locally with Blob URLs.
• The optional FRED action makes GET requests containing only public series identifiers. It is reference-only and never includes calculator inputs.
• Property information is manual entry only.

Public configuration

PUBLIC_DEFAULTS explicitly defines every field accepted by the public model. The fictional values were created independently for this page. There is no fallback to private configuration.

Keeping implementations aligned

The public model deliberately implements a reviewed subset of the research model: fixed-rate amortization, equity, accessible assets, effective investment-sale tax, home-sale proceeds, inflation, recurring ownership costs, household cash flow, reserve funding, holding periods, and synthetic stresses. Changes to those concepts should be made in the private Python engine first, then ported deliberately to the public JavaScript model and checked with python scripts/test_housing_public_model.py.

The test compares the browser mortgage formula with an independent Python calculation and uses only the public synthetic fixture. It also covers amortization/equity identities, taxable withdrawals, sale proceeds, infeasibility, stresses, and sensitivity direction.