Watch your money grow with the power of compound interest over time
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Enter your starting amount (initial investment), how much you plan to add each month, the expected annual rate of return, how often interest compounds, and how many years you plan to invest. The calculator instantly shows your projected final balance.
The chart visualizes how your total balance grows over time, with contributions and interest earned shown separately so you can see exactly how much compound interest contributes to your wealth.
Compound interest is interest earned on both your original principal and on previously accumulated interest. The formula is A = P(1 + r/n)^(nt), where P is principal, r is the annual rate, n is compounding frequency, and t is time in years.
The key insight is that time is the most powerful variable. Starting five years earlier can result in significantly more wealth than increasing your monthly contribution, because those extra years give compound interest more time to work.
Regular contributions amplify the effect dramatically. Even modest monthly additions, compounded over decades, can grow to substantial sums.
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by your annual rate of return. At 8% returns, your money doubles roughly every 9 years (72 / 8 = 9).
The S&P 500 has historically averaged about 10% per year before inflation, or about 7% after inflation. A diversified portfolio might return 6-8% long-term. More conservative investments like bonds return 3-5%.
More frequent compounding (daily vs. annually) produces slightly higher returns, but the difference is small. The most important factors are the rate of return, how much you contribute, and how long you invest.
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