edb4d11352
Some checks are pending
Add a Monte-Carlo "FIRE number" solver so the wealth dashboard can show a £ countdown to retirement across life-stage cases, in today's money. Viktor wants to see, per country, how far his net worth is from being able to retire for good under three cases — Solo (his spend ×1.5), Household (+Anca ×1.5), Family (+2 kids) — with cost-of-living re-scaling per country and a 99% Guyton-Klinger success bar. - spend_model: per-Case real-GBP spend, COL-scaled (rent + non-rent essentials scale by country; Holidays fixed), ×1.5 safety. Constants sourced live from actualbudget (Viktor) / on-record (Anca). - geo: city -> tax jurisdiction (nomad fallback). - fire_target: binary-search the smallest LIQUID net worth where GK reaches the bar; pension modelled as a tranche unlocking at ~57, kids ramp + optional home as cashflows. New fire_target table (migration 0007) + idempotent upsert. - recompute-fire-targets CLI: solve every Case x country and persist for Grafana. - CONTEXT.md glossary + ADR-0001 (why MC-threshold on liquid NW, not 25x spend). Reuses the existing simulator unchanged (its cashflow hooks already supported pension/kids/home). 345 tests pass; mypy + ruff clean. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
30 lines
1.7 KiB
Markdown
30 lines
1.7 KiB
Markdown
# FIRE number via Monte-Carlo NW-threshold on the liquid pot
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We compute each Case's target net worth (its "FIRE number") by searching net
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worth for the smallest value at which Guyton-Klinger reaches a 99% Monte-Carlo
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success rate — **not** a fixed safe-withdrawal-rate multiple (e.g. 25× spend).
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A fixed multiple cannot honour the structure the engine already models: the
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rising 30→70 equity glide, per-jurisdiction taxes drained from the portfolio,
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the kids-cost ramp, an optional one-time home purchase, and a workplace pension
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that is locked until ~57. Our block-bootstrap's empirical perpetual SWR is also
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~2.5–3%, materially below the textbook 4%, so a 25× multiple would understate
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the number anyway.
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The solver seeds on **liquid** net worth — it excludes the Fidelity workplace
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pension (inaccessible until ~57) and injects that pension as a grown lump at age
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57. Early-retirement sequence risk is funded only by spendable assets, so seeding
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total net worth would overstate safety exactly where the 99% bar is decided.
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## Consequences
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- A vectorised NW search (binary search over `initial_portfolio`, monotone
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because the GK year-0 draw is an absolute real amount) populates a
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`fire_target` table, one row per (Case × country × with-home).
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- Targets vary by country through **both** COL-scaled spend and the destination
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tax regime (the simulator drains tax from the portfolio since 2026-05).
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- The Grafana countdown reads `fire_target` for the selected country and diffs
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it against current liquid net worth from `account_snapshot`.
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- Pension growth to age 57 is modelled deterministically (current value
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compounded at an assumed real rate), not per-path — a conservative
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simplification, revisitable if it ever binds.
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