The assumptions are part of the answer.

Retirement Gap expresses a retirement scenario as supported monthly spending in today’s purchasing power. It is educational math—not a prediction or recommendation.

Projection

Let P be tracked retirement savings, C the typical monthly contribution, n the number of months until retirement, and r the effective monthly real return. Retirement Gap calculates the future value as P × (1 + r)ⁿ + C × (((1 + r)ⁿ − 1) ÷ r). When r is zero, it uses P + C × n.

Supported monthly spending equals the projected balance multiplied by the annual withdrawal-rate assumption, divided by 12, plus other expected monthly retirement income. The gap is the amount, if any, between that result and desired monthly spending.

Required monthly saving

Retirement Gap first calculates the portfolio needed to support the spending target after other retirement income: max(0, (desired monthly spending − other monthly income) × 12 ÷ withdrawal rate). It then grows today’s savings to retirement using the real-return assumption. The remaining portfolio need is divided by the same future-value factor used for one end-of-month contribution every month until retirement. This required pace is based on the life and timeline entered; the current contribution is shown only for comparison.

Today’s dollars

The return assumption is real—after inflation—so the current balance, desired spending, projected balance, and supported spending use the same purchasing-power frame. Retirement Gap does not separately predict inflation.

Contribution pace

For the current calendar year, Retirement Gap subtracts both the amount you report contributing before setup and later daily contributions from the editable annual target. It divides the non-negative remainder across the current and future months still available. Daily contributions reduce the remainder without closing the current month. Marking the month complete removes it from the remaining-month count and redistributes the pace across future months.

What is deliberately absent

Retirement Gap does not model taxes, fees, market volatility, sequence-of-return risk, longevity, Social Security rules, contribution limits, account types, employer matching, or asset allocation. Use a qualified professional for decisions that require those factors.

Defaults

Version 1.0 starts with a 3% real annual return and a 3.5% withdrawal rate. Both are editable scenario assumptions and neither is a promise of future performance.