Retirement Planning, Modeled Like a CFO
A household-scale financial projection engine that handles the parts most calculators skip — taxes, RMDs, Social Security taxability, Monte Carlo risk, and life-stage healthcare costs — all in a single scenario you can edit and re-run in real time.
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What it does
Models a household's full retirement horizon year-by-year — income streams, savings vehicles, accounts, asset allocation, taxes, and expenses — then simulates thousands of alternative market paths to show the range of likely outcomes.
Why it exists
Most online retirement calculators stop at “can I afford it?” They ignore taxes, withdrawal order, RMDs, healthcare phases, and return variance. This tool models all of it, so the answer reflects what actually happens in retirement — not a rounded average.
How it was built
Built with AI agents in iterative passes — data model first, projection engine next, then tax, RMD, and Monte Carlo layers. Every edge case (job changes, gap coverage, home sales, survivor benefits, inherited IRAs) was added by describing the scenario and letting agents implement it.
What the engine models
Full tax engine
Federal + state income tax, FICA, LTCG, Social Security taxability thresholds, standard deduction with 65+ bonus, and NIIT — all recomputed every projection year.
RMDs & Inherited IRAs
Uniform Lifetime and Single Life tables applied automatically, plus the 10-year rule for inherited IRAs, feeding correctly into ordinary-income tax.
Social Security
Per-person start age, survivor benefit (max of own vs 50% of deceased spouse), and automatic inclusion in provisional income for SS taxability math.
Life stages
Housing costs and a four-phase healthcare timeline per person (employer → pre-Medicare → Medicare → acute care) derived from income and life expectancy.
Withdrawal strategies
Tax-smart or conventional ordering. Iterative solver handles the chicken-and-egg of withdrawals causing taxes causing more withdrawals.
Monte Carlo
Stochastic returns drawn from each asset class's historical mean and standard deviation, rendered as percentile bands so you can see the range — not just the median.
Goal scorecard
Pass/warn/fail readout for each household goal (travel budget, legacy target, vacation home, etc.) evaluated against the projection.
Home sales & §121
Model a primary residence sale with the §121 exclusion applied correctly, and roll proceeds into the right account automatically.
Inside the app
Technology Stack
Frontend
- React 19 + TypeScript
- Vite build system
- Recharts visualizations
- Web Workers for Monte Carlo
Engine
- Pure-TS projection core
- Iterative tax solver
- IRS RMD tables built in
- Scenario JSON import/export
Persistence
- localStorage (default)
- Firebase (optional sync)
- JSON scenario files
- No server required
Infrastructure
- GCP Cloud Run
- Cloud Build CI/CD
- Nginx static serving
- Firebase Hosting-ready