Compound Growth Calculator

How to use this calculator

This calculator answers: What could my savings grow to, and how much of it is growth versus my own contributions?

Why this matters: Small changes in time, contributions, or return compound into life-changing differences — seeing the split between your money and growth makes that real.

Set Starting amount ($), Monthly contribution ($), Expected annual return (%), Years invested, and Compounding frequency.
Everything recalculates live as you type — no button needed.
Read “Your projection” and “Where the money comes from” to see growth vs. your own contributions. Try a 3% vs 5% return — or five extra years — to see compounding at work.

Your plan

Starting amount ($) What you're beginning with. Example: 10,000.

Monthly contribution ($) Added at the end of each month. Example: 500.

Expected annual return (%) Nominal, before inflation. Example: 7. Try 5 and 9 too — the range matters more than the point estimate.

Years invested How long the money stays invested. Example: 30.

Compounding frequency How often returns are credited. Monthly is the standard assumption.

Cost-of-waiting: years delayed Compare starting now vs. starting this many years later. Example: 5.

How the projection works

Month-by-month simulation: your balance grows each month and your contribution lands at month end, so every dollar starts compounding the month it arrives.
Compounding frequency: the annual return is converted to an equivalent monthly rate — (1 + r/f)^(f/12) − 1 — so quarterly and annual compounding flow through the monthly simulation rather than being approximated.
Cost of waiting: the same plan run twice — once starting now, once starting N years later with the remaining years. The gap is almost always larger than the contributions you skipped, because the earliest dollars compound the longest.
What it leaves out: taxes, fees, and inflation. A 1% annual fee on a 7% return doesn't cost you 1% — over 30 years it eats roughly a quarter of the ending balance.

Frequently asked questions

How is compound growth calculated?

Your starting balance and each monthly contribution grow at a monthly-equivalent rate derived from the annual return you enter. The calculator simulates month by month, so every contribution starts earning from the month it lands.

What annual return should I assume?

There is no single right number. US stocks have averaged roughly 10% nominal (about 7% after inflation) over very long periods, but any single decade can look very different. Many planners run 6–8% nominal for a stock-heavy mix and 3–4% for bonds or cash. Try a low, middle, and high case rather than trusting one forecast.

What is the cost of waiting?

It compares starting now versus starting N years later with the same contributions. Because early contributions compound the longest, waiting even a few years can cost far more than the skipped contributions themselves.

Does this include taxes or fees?

No. The projection is before taxes, fees, and inflation. A 1% annual fee or a higher-tax account can meaningfully reduce the real result.

Is the return guaranteed?

No. The calculator assumes the same return every year. Real markets bounce around, and the sequence of returns matters — especially once you start withdrawing.