Compound Interest & Investment Growth Calculator

Forecast compound interest, future portfolio value, and recurring contributions over any investment horizon.

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Initial Principal ($):

Monthly Contribution ($):

Annual Return Rate (%):

Investment Period (Years):

$213,767Future Portfolio Value

$82,000Total Principal & Deposits

$131,767Total Compound Interest Earned

Growth Breakdown

Deposits (38%)

Compound Growth (62%)

In 20 years, your $10,000 initial deposit and $300 monthly savings will grow into $213,767.

The Mathematical Power of Compounding, Reinvestment, and Wealth Accumulation

Compound interest is interest calculated on the initial principal, which also includes all of the accumulated interest from previous periods. Unlike simple interest, compound interest results in exponential growth over extended time horizons.

The Future Value Annuity Formula

FV = P * (1 + r/n)^(nt) + PMT * [ ((1 + r/n)^(nt) - 1) / (r/n) ]

P: Starting lump-sum principal
PMT: Regular monthly contribution
r: Annual nominal rate of return (decimal)
n: Compounding frequency per year (12 for monthly)
t: Total investment horizon in years

Frequently Asked Questions (FAQ)

The Rule of 72 is a quick estimation shortcut: divide 72 by the annual return rate to estimate how many years it takes for an investment to double (e.g. 72 / 8% = ~9 years).

Over the last century, broad market indices like the S&P 500 have delivered an average nominal annualized return of approximately 10% before inflation.