Fire & Strike

Fire & Strike is a retirement calculator for the FIRE community with two use cases: project your current pace as a Monte Carlo fan chart (p10/p50/p90 portfolio paths vs age, each stamped with its FIRE-crossing age), and solve a STRIKE plan — the extra yearly contribution so the median path reaches your target retirement age.

Open Fire & Strike · Source on GitHub

Highlights

  • Honest projections: seeded, reproducible Monte Carlo (Mulberry32 normal streams, default 7%/18% stocks, 2.5%/6% bonds) — percentiles instead of a single confident date.
  • STRIKE solver: binary search over extra yearly contribution until the p50 path crosses FIRE exactly at the declared age — “50% chance” confidence by design.
  • Draft-then-calculate inputs: never clamped mid-typing, warnings + aria-invalid on invalid drafts, collapsed Advanced assumptions.
  • DDD ubiquitous language + onion architecture: pure domain services behind ports, use cases in application, arch-unit boundaries.test.ts guarding the layers.
  • Built by the Ralph loop: spec of record → ordered TDD tasks → agent iterations gated by lint + typecheck + tests → GitHub Pages deploy on every push.

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