Limitations
RetireNumber stress-tests your plan. It doesn't predict the future. This page covers what the model can and can't do, so you know where to trust it and where to apply your own judgment.
Markets & projections
Past ≠ future
Backtests use Shiller data from 1928 to today. The future can be better or worse than any historical period. We don't predict returns.
Assumptions are inputs, not guarantees
Default return (6.5%), inflation (3%) and fees (0.25%) are configurable starting points. Your real outcomes will differ. That's why we show ranges, not a single line.
Monte Carlo is a statistical model
We run 1,000 random return paths to show what's plausible, not what will happen. The distribution may not match the next 30 years.
We stress-test your plan; we don't forecast the market.
Policy & rules
Social Security
We use current law and your inputs (earnings, claiming age). Benefit formulas, full retirement age and trust fund rules can change. We don't model future legislation.
Taxes
Federal and state tax rules are modeled as they exist today. Tax law changes (e.g. TCJA sunset, new brackets) aren't reflected until you update your plan.
Medicare & healthcare
We don't model Medicare premiums, IRMAA surcharges or long-term care costs. These can materially change retirement spending.
We use today's rules. When rules change, update your plan.
Your personal situation
Longevity
We use the life expectancy you enter (or a default). We don't model health, family history or tail risk like living well past 100.
One-off events
Disability, divorce, windfalls, major gifts or unexpected care costs aren't automatically modeled. Use the events tool where the product supports it.
Spending
We use the spending and withdrawal strategy you choose. Real spending is lumpy and uncertain. We model the math, not every possible life path.
The plan is only as good as the inputs and life path you assume.
What we don't model
Behavior
Panic selling, market timing or changing strategy mid-crash. The model assumes you stick to your plan.
Asset allocation shifts
We typically assume a single blended return. We don't auto-rebalance or model a glide path from stocks to bonds unless you set that up manually.
Black swans
Regime changes, political upheaval or structural breaks that have no precedent in the historical data.
We model portfolio math and policy; we don't model human behavior or tail events.
Not financial advice
RetireNumber is for education and planning only. We don't provide investment, tax or legal advice. Past performance does not guarantee future results. Please consult a licensed financial professional before making decisions about investments, taxes or estate planning.