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Under the hoodFor the curious and the careful. A look at the engine, the tax modeling, the privacy architecture and the validation that sit behind every number — plus the full documentation to download.
The core is a transparent simulation that steps through retirement one month at a time. Configuration flows from your inputs through a clear pipeline — buildPhaseConfig → calcAllPhases → calcPhase → simPhase — applying compound growth, withdrawals and income for each phase.
Because it’s deterministic, the same inputs always produce the same results, and every figure can be traced back to the rule that produced it. Tax brackets, deductions, FPL thresholds and Medicare costs are each inflation‑adjusted per phase.
US federal brackets with the senior add‑on, Social Security provisional‑income taxation done the IRS way, NIIT and IRMAA with a two‑year lookback, plus flat state tax. International regimes for the UK, Canada and Australia apply the US Foreign Tax Credit under treaty rules.
Thousands of randomised market paths with configurable volatility and — importantly — randomised inflation in every run, for a more honest distribution of outcomes. A historical backtest replays real US market history since 1928 against your plan.
The entire app is one self‑contained HTML file. State lives in your browser’s local storage; nothing is transmitted. Optional AI runs under your own API key, called directly from your browser — there’s no WebNomad server in the loop and no account to create.
The planner ships with a golden‑master self‑test that re‑runs the engine against fixed fixture plans and diffs the results against known‑good values — catching silent calculation drift instantly. Coverage spans four national tax regimes, Social Security claim‑age splits, RMD/NIIT/ACA, early retirement, Roth conversions, pensions, lump sums and goals.
Information first, accessible by default. A WCAG‑AA colour system, high‑contrast theme, adjustable text up to 135% and reduced‑motion support make long planning sessions comfortable. The figures distinguish clearly between nominal (future dollars) and real (today’s money) so you’re never misled by inflation.
Full documentation, openly available — because a tool you can question is a tool you can trust.
A real, worked plan exported from the planner — see the output for yourself.
Download PDF →Also available: a Best‑Practices guide — download PDF.
