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The user noticed the "Annual spending" field was a no-op for Trinity,
GK, VPW, VPW+floor — the strategies internally hardcoded the year-0
withdrawal as `initial_portfolio × initial_rate` (4% / 5.5%) and
ignored what the user typed. Two fixes:
(1) Trinity + GK now use state.initial_withdrawal (= the user's
spending_target) as the year-0 draw. GK's guardrail anchor
becomes the implied initial rate (initial_withdrawal /
initial_portfolio), so the rule shape adapts to the user's
chosen rate. Both strategies still fall back to their preset
rate × initial_portfolio when initial_withdrawal isn't set
(test paths). VPW and VPW+floor stay algorithmic — they're
"withdraw-what's-sustainable" by design and don't take a
spending input.
(2) New "custom" preset (SpendingPlanStrategy) exposing all the
knobs:
- initial_spend = "Annual spending" input
- annual_real_adjust_pct = scale last year's withdrawal by N%
each year (0 = constant real £, +0.02 = 2%/yr healthcare
creep, -0.005 = -0.5%/yr slow-down with age)
- guardrail_threshold_pct = if portfolio falls below X% of
starting NW, trigger a cut (None = disabled)
- guardrail_cut_pct = cut last year's withdrawal by Y% each
triggered year
Adjust applies first, then guardrail cut — so a triggered year in
+2% adjust mode goes 40k → 40.8k → 36.7k.
UI: "custom" added to the strategy dropdown; when selected, three
extra fields appear (annual real adjustment %, guardrail trigger
threshold, guardrail cut size) with hints. The existing inputs
(spending, NW seed) drive year 0 across all strategies that use
them. About-the-model panel updated.
10 new tests on SpendingPlanStrategy + adjusted GK tests for the
new spending_target-aware behaviour. 209 backend tests + 7
frontend tests. mypy + ruff + tsc all pass.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
30 lines
1.2 KiB
Python
30 lines
1.2 KiB
Python
"""Constant-real-£ withdrawal (the classic 4% rule shape).
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Withdraw `state.initial_withdrawal` in year 0, then keep that real-£
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amount fixed for the rest of retirement. In a 4% / £1M setup the year-0
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draw is £40k, then £40k real every year after. The strategy's
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`initial_rate` is kept only as a fallback for callers that don't feed
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`state.initial_withdrawal`.
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"""
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from __future__ import annotations
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from fire_planner.strategies.base import StrategyState, WithdrawalStrategy
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DEFAULT_INITIAL_RATE = 0.04
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class TrinityStrategy(WithdrawalStrategy):
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name = "trinity"
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def __init__(self, initial_rate: float = DEFAULT_INITIAL_RATE) -> None:
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self.initial_rate = initial_rate
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def propose_withdrawal(self, state: StrategyState) -> float:
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if state.year_idx == 0:
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# Year 0 = the user's target spending. Falls back to
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# initial_rate × initial_portfolio if no target was provided
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# (zero or missing) for backwards compatibility.
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if state.initial_withdrawal > 0:
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return state.initial_withdrawal
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return state.initial_portfolio * self.initial_rate
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return state.last_withdrawal
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