Compound Growth Calculator
Time plus steady contributions beats timing. Enter what you have, what you can add each month, and a return assumption — see the projected future value, how much of it is growth versus your own money, and what waiting a few years actually costs.
Your plan
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 a monthly-equivalent rate — (1 + r/f)^(f/12) − 1 — so quarterly and annual compounding are handled exactly, not 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.