How to Estimate Your Retirement Savings Goal

Retirement savings goals can feel abstract precisely because the deadline is decades away — but the math behind getting there is the same compound growth math that applies to any long-term goal, just stretched over a longer timeline where the effect of compounding becomes dramatic.

Step 1: Estimate what you'll need

A commonly cited rule of thumb is that you'll need roughly 25 times your desired annual retirement spending saved (based on a 4% annual withdrawal rate assumption). If you want $40,000/year in retirement income from savings, that points to a target of roughly $1 million — a useful starting estimate, though personal circumstances (other income sources, expected lifestyle, healthcare costs) shift the real number.

Step 2: Work out what you need to save now

With a target number and a timeline (years until retirement), the question becomes: how much do I need to contribute regularly, given expected investment growth, to reach that target? This is exactly what compound interest math answers.

FV = P × (1+r)ⁿ + PMT × (((1+r)ⁿ − 1) ÷ r)
where P = current savings, PMT = regular contribution, r = rate per period, n = number of periods

The Compound Interest Calculator runs this projection directly — enter your current savings, planned monthly contribution, an expected average return, and your time horizon, and it shows the projected future value alongside a year-by-year growth chart.

Why starting earlier matters disproportionately

Because compounding is exponential, not linear, the gap between starting at 25 versus 35 is far larger than ten years' worth of contributions alone would suggest — the early contributions have ten extra years to compound, which often accounts for a substantial share of the eventual difference in final balance.

Revisit the number periodically

Expected returns, retirement timeline, and lifestyle expectations all shift over years and decades. Treat any retirement projection as a working estimate to revisit every few years — not a number calculated once in your twenties and never reconsidered.