Calculation Methodology

How our retirement calculators work

RetirementPlanCalc uses transparent, simplified formulas to compare planning scenarios. Inputs are processed in your browser. The tools do not load account balances, live returns, benefit estimates, inflation data, or current contribution limits automatically.

Dollar displays are rounded to the nearest whole dollar. Calculations retain greater precision internally. Years are whole numbers; contribution and withdrawal periods use 12 months per year. Defaults are examples rather than forecasts or recommendations.

Savings and monthly contribution tools

The savings, contribution, and homepage tools use a nominal annual return divided by 12. Let r be that monthly rate and n the number of months. Starting savings P grow to P × (1 + r)ⁿ. End-of-month deposits C accumulate to C × ((1 + r)ⁿ − 1) ÷ r.

At a zero rate, the result is P + C × n. To solve for required contributions, subtract projected starting-balance growth from the future-dollar target and divide by the accumulation factor. A negative required contribution is displayed as zero.

Inflation and spending targets

The inflation tool multiplies a current amount by (1 + inflation) raised to the number of years. Dividing a future face amount by the same factor estimates its current purchasing power under the chosen assumption.

The goal tool and homepage subtract other annual income from annual spending, with the gap floored at zero. They inflate that gap to retirement and divide by the chosen withdrawal-rate fraction. Spending and other income are assumed to rise at the same rate. This heuristic does not test longevity or success probability.

Income and withdrawal projections

The income tool converts effective annual investment return and inflation into a real annual return: (1 + return) ÷ (1 + inflation) − 1. It converts that to an effective monthly real rate and calculates a level end-of-month payment that spends the portfolio down over the selected period.

At zero real return, portfolio income equals balance divided by months. Other income is assumed to preserve purchasing power throughout the period. A fixed pension without inflation adjustments requires separate analysis.

The withdrawal tool grows the balance each month using an effective monthly return, then subtracts the scheduled withdrawal. The withdrawal rises at each new 12-month year, starting in month 13. Payments cannot exceed the available balance. Depletion is checked monthly, and a final partial payment may occur.

FIRE and employer matching

The FIRE tool divides annual spending by a selected withdrawal-rate fraction. It then applies an effective real monthly return and fixed real monthly deposits until the target is reached or 100 years pass. Fixed real deposits imply that nominal deposits rise with inflation.

The employer-match tool supports one tier. Employer match equals eligible pay multiplied by the lesser of employee contribution percentage and match-eligible pay percentage, multiplied by the employer’s matching percentage. It does not apply IRS or plan limits, vesting, paycheck timing, or true-up provisions.

Validation and limitations

Inputs are checked for missing values, finite numbers, allowed ranges, and whole-year requirements. The homepage requires planned retirement age to exceed current age. Editing an input hides the previous result so it is not mistaken for a result based on new values.

These tools do not model taxes, contribution eligibility, market volatility, required minimum distributions, account-access rules, fees separately from your chosen net return, or changing personal expenses. A constant-return model does not capture sequence-of-returns risk.

Report a concern with the URL, inputs, and expected result to contact@retirementplancalc.com. Explain whether you are questioning arithmetic, an assumption, or a missing real-world feature.