NYC residents pay, on a capital-gain distribution, roughly 20% federal
+ 3.8% NIIT + 6.85-9.65% NY + 3.876% NYC = ~34-37% — the old model's
flat 20% understated the real after-tax drag of high-distribution
funds for this user by ~15 points on exactly the flows that matter.
tax.py: new niit + sl_rate params (decimals). sl_rate is the
state+local marginal rate applied at ORDINARY rates to every flow —
state and local have NO preferential cap-gain rate, so the composite
is lt_rate+niit+sl_rate on cap-gain dists, div_rate+niit+sl_rate on
dividends, and (st/lt_rate)+niit+sl_rate on realized gains.
app.py: two new sidebar fields (persisted in settings.json), wired
through _compute_portfolio's cache key.
tests/test_tax.py: 3 new cases (capg and div composite rates,
net-taxed realized ST gains/losses at st+NIIT+SL).
README: NYC rate note with the 2025 IT-201 schedule values (NYC 3.876%
over $50k; NY 6.85% at $215,400-$1.077M, 9.65% at $1.077M-$5M,
single filer) and the composite example.
Greg Pomerantz
19b33d5a18