SimuPlan

Trust explainer

Methodology & Validation

Retirement math you can inspect.

SimuPlan is designed to show the assumptions, calculations, and tradeoffs behind each result. The goal is not to predict the future with certainty, but to make retirement planning clearer, more transparent, and easier to test.

Inputs

Balances, income, spending, retirement age, assumptions

Assumptions

Inflation, growth, taxes, withdrawals, Social Security, healthcare

Calculations

Projections, tax estimates, simulations, scenario comparisons

Outcomes

Balances, shortfall/surplus, success probability, drivers, insights

What SimuPlan models

  • Long-term retirement projections
  • Contributions, spending, withdrawals, and growth
  • Inflation-adjusted planning assumptions
  • Tax-aware retirement cash flows
  • Roth conversion tradeoffs
  • Monte Carlo and historical simulations
  • Scenario comparisons and plan tracking

What SimuPlan does not claim

  • It does not predict the future
  • It does not guarantee retirement success
  • It does not replace a financial advisor
  • It does not replace tax-preparation software
  • It should be used for planning, education, and scenario exploration

Projection and tax engines

SimuPlan's deterministic projection engine builds a baseline retirement path using starting balances, contributions, spending, inflation, growth assumptions, withdrawals, taxes, and ending balances. The tax engine is designed for long-term planning and scenario analysis, not tax filing.

Projection engine

  • Starting balances
  • Contributions and income
  • Spending and inflation
  • Withdrawals and growth
  • Ending balances

Tax engine

  • Federal and state tax estimates
  • Social Security treatment
  • Roth conversion impacts
  • Taxable income and withdrawals
  • Planning-grade tax calculations

SimuPlan is not tax-preparation software. Tax calculations are intended for planning and comparison, not filing returns.

Tax transparency at a glance

SimuPlan includes planning-grade tax estimates so users can compare retirement scenarios with more context. The goal is practical transparency, not tax filing or a dense tax-law manual.

  • Uses loaded federal, state, ACA/MAGI, and IRMAA assumptions where they affect retirement planning.
  • Shows when taxes, MAGI, RMDs, and healthcare thresholds may matter for a scenario.
  • Lets Scenario Lab stress-test higher future tax rates with a simple rate-increase test.
  • Does not try to forecast future tax law or replace tax software.

Inside the app, the Methodology view shows a more detailed modeled-vs-simplified breakdown for users who want the deeper assumptions.

Simulation engines

Randomized Monte Carlo

Runs many randomized future market paths to help show how a plan might behave across a range of possible outcomes.

What it teaches: how sensitive the plan may be to uncertainty.

Historical testing

Tests plans against historical-style market windows to show how different return environments could affect long-term results. This uses a Robert Shiller-based market dataset refreshed through the latest complete calendar year available in SimuPlan.

What it teaches: how past market environments would have challenged the plan.

Market replay

Replays major market events as educational stress tests so users can see how difficult periods may affect a plan.

What it teaches: why sequence-of-returns risk matters.

Benchmarking and validation

During development, SimuPlan's projection, tax, randomized Monte Carlo, and historical simulation engines were benchmark-tested against other respected planning tools under comparable assumptions. The goal was to keep results within a tight tolerance where assumptions overlap, investigate differences, and harden the model.

  • Compared against respected planning tools where assumptions could be aligned
  • Checked deterministic projections, taxes, Monte Carlo outputs, and historical simulation behavior
  • Investigated differences caused by taxes, inflation, withdrawal order, rounding, and tool-specific assumptions
  • Focused on consistency, transparency, and explainability rather than false precision

Different tools can still produce different results because they may use different assumptions, tax simplifications, return models, withdrawal ordering, or rounding rules.

Why retirement tools can disagree

Two retirement calculators can both be reasonable and still produce different answers. The assumptions matter.

  • Inflation assumptions
  • Market return assumptions
  • Tax assumptions
  • Social Security assumptions
  • Withdrawal order
  • Roth conversion handling
  • Healthcare assumptions
  • Rounding and timing rules

See the model in action.

Explore the demo plan to see how SimuPlan connects assumptions, projections, simulations, and plain-English explanations before entering your own numbers.

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