plan529lab 0.1.0

529 vs taxable brokerage after-tax tradeoff engine

plan529lab

A Python package for evaluating the after-tax tradeoff between investing through a 529/Qualified Tuition Program (QTP) and a taxable brokerage account for education savings.

This is not a simple "529 penalty calculator." It is a scenario engine that compares after-tax outcomes across multiple future states — including qualified education use, nonqualified withdrawal, beneficiary change, and Roth IRA rollover paths.

Disclaimer: This package is for educational and analytical purposes only. It is not tax, legal, or investment advice. Tax outcomes depend on facts, jurisdiction, and future law changes. Consult a qualified tax professional for your situation.

Why This Exists

Public discussion of 529 plans often oversimplifies the tradeoff. Common claims that 529s are "risky" because of "penalties" miss key nuances:

• Only the earnings portion of a nonqualified withdrawal is taxable — contributions/basis come back tax-free
• The 10% additional tax applies to the amount included in income, not the entire withdrawal
• Qualified expenses must be reduced by tax-free educational assistance and expenses used for AOTC/LLC
• State tax benefits, recapture rules, and the Roth rollover path materially affect the comparison

This package makes these interactions explicit and quantifiable.

Installation

pip install plan529lab

For development:

pip install -e ".[dev]"

Requires Python 3.11+.

Quick Start

Python API

from plan529lab.api import analyze_tradeoff
from plan529lab.io.yaml_loader import load_config
from plan529lab.state_rules.no_income_tax import NoIncomeTaxStateRule

config = load_config("examples/washington_no_income_tax.yaml")
result = analyze_tradeoff(config, state_rule=NoIncomeTaxStateRule("WA"))

print(result.explain())
print(f"Delta: ${result.delta:,.2f}")
print(f"Break-even probability: {result.break_even_qualified_use_probability:.1%}")

Monte Carlo Simulation

from plan529lab.api import run_monte_carlo
from plan529lab.models.monte_carlo import MonteCarloConfig, StochasticAssumptions

mc_config = MonteCarloConfig(
    n_paths=10_000,
    seed=42,
    stochastic=StochasticAssumptions(return_std=0.15),
)
mc_result = run_monte_carlo(config, mc_config)
print(f"P(529 wins): {mc_result.prob_qtp_wins:.1%}")
print(f"Mean delta: ${mc_result.mean_delta:,.2f}")

Sensitivity Analysis

from plan529lab.api import run_sensitivity

result = run_sensitivity(config, "qualified_use_probability", [0.0, 0.25, 0.5, 0.75, 1.0])
for v, d in zip(result.param_values, result.deltas):
    print(f"  p={v:.0%}: delta=${d:,.0f}")

CLI

# Deterministic analysis
python -m plan529lab analyze --config examples/washington_no_income_tax.yaml

# Monte Carlo simulation
python -m plan529lab monte-carlo --config examples/washington_no_income_tax.yaml --n-sims 10000 --seed 42

# Sensitivity analysis
python -m plan529lab sensitivity --config examples/washington_no_income_tax.yaml \
    --param qualified_use_probability --min 0 --max 1 --steps 11

# Break-even probability
python -m plan529lab breakeven --config examples/washington_no_income_tax.yaml

# State rule info
python -m plan529lab state-info WA

Configuration

Scenarios are defined in YAML files. See examples/ for templates.

tax_profile:
  ordinary_income_rate: 0.35
  ltcg_rate: 0.15
  qualified_dividend_rate: 0.15

portfolio_assumptions:
  annual_return: 0.07
  dividend_yield: 0.015
  qualified_dividend_share: 0.95
  turnover_realization_rate: 0.05

scenario_policy:
  qualified_use_probability: 0.75

horizon_years: 18

State Rules

The package uses a plugin architecture for state-specific tax treatment:

• NoIncomeTaxStateRule — for WA, TX, FL, NV, SD, WY, AK, TN, NH
• GenericDeductionStateRule — models a state income tax deduction on 529 contributions
• GenericCreditStateRule — models a state tax credit on 529 contributions

Generic rules do not reflect any specific state's exact rules, caps, or conditions.

Assumptions and Limitations

• Annual timesteps with start-of-year contributions
• Simplified taxable account model (no lot-level accounting, wash-sale rules, or AMT)
• Tax rates are assumed constant over the horizon
• Roth rollover uses one-shot eligibility estimate (not year-by-year staged rollover)
• Monte Carlo treats dividend yield and turnover as per-path constants (not per-year)
• State rules are generic unless specifically implemented

Development

# Install dev dependencies
pip install -e ".[dev]"

# Run tests
pytest -v

# Lint
ruff check .

# Type check
mypy .

License

MIT