Compound interest is the quiet engine behind most lasting wealth. Your money earns a return, then that return starts earning returns of its own, and the growth curve bends upward the longer you leave it alone. Move the sliders below to watch your own numbers play out.
The calculator starts with your opening balance and walks forward one month at a time. Each month it multiplies your balance by one twelfth of your annual return, then adds your monthly contribution. Repeating that simple step hundreds of times produces the curve you see in the chart.
The gap between the two lines is the part your money earned on its own. Early on the gap looks small and unimpressive. Give it fifteen or twenty years and the earnings often grow larger than everything you put in, which is exactly why starting early matters more than starting big.
A long run figure of 6 to 8 percent is a common planning assumption for a diversified stock portfolio, which is why the slider defaults to 7. Use something lower, such as 4 or 5 percent, if your money sits in bonds or savings accounts.
No. The chart shows raw growth before taxes and inflation. For a rough inflation adjusted view, subtract about 3 percentage points from your expected return and run it again.
Monthly. Your annual rate is divided by twelve and applied every month, with contributions added at the end of each month. Most real world accounts compound monthly or daily, so the results will be very close.
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