Calculator Methodology

RetirementMetric calculators are educational models. This page explains the principles we use so readers can understand what the outputs do—and do not—represent.

Inputs and assumptions

Calculators use the numbers entered by the reader together with the assumptions shown on each tool. Common inputs include starting balance, contribution amount, time horizon, annual return, interest rate, withdrawal rate and tax rate. We do not treat a default value as a forecast.

Compounding and contribution timing

Growth calculators generally model periodic compounding and recurring contributions. Small differences in contribution timing, compounding frequency, fees and market sequence can materially change real-world outcomes. Results should be treated as planning illustrations rather than precise forecasts.

Investment returns

Any assumed return is hypothetical. Markets are volatile, returns are not guaranteed, and actual portfolios can experience losses. A constant annual-return model cannot reproduce the sequence of gains and losses experienced by a real investor. Testing conservative, middle and optimistic assumptions can provide a more useful range.

Taxes, fees and inflation

Unless a calculator explicitly includes a field or explanation for taxes, investment expenses or inflation, those factors should not be assumed to be fully modeled. Tax treatment depends on account type, income, jurisdiction and future law. Fees vary by investment and provider.

Retirement withdrawals

Withdrawal-rate calculations translate a portfolio value into an illustrative income amount. They do not guarantee that a portfolio will last for a particular period. Longevity, market sequence, inflation, taxes, spending changes and asset allocation can all affect sustainability.

Debt and mortgage calculations

Debt tools are mathematical estimates based on entered balances, rates and payments. Real lender calculations may differ because of daily interest, fees, variable rates, escrow, payment timing, promotional terms or other contract provisions.

Rounding

Displayed results may be rounded for readability. Intermediate calculations can use greater precision, so manually reproducing a result from rounded display values may produce a small difference.

How to use the results

Use calculator results to explore scenarios and questions to investigate further. Do not use them as a substitute for account statements, lender disclosures, plan documents, tax calculations or individualized advice from a qualified professional.

See also our Editorial Policy and Financial Disclaimer.