Project investment growth over time with initial amount, monthly contributions, and variable return rates.
This calculator follows an investment from its starting balance through a chosen time horizon, adding a recurring monthly contribution and applying the return rates entered for the applicable periods. Allowing rates to vary makes it useful for testing changing assumptions instead of relying on one annual rate throughout. The most common misreading is treating the ending balance as investment profit. That balance includes the initial amount and every monthly contribution, so growth should be separated from money the investor supplied.
A concrete input and expected output from the current implementation.
Input
Initial amount: $1,000 Monthly contribution: $100 Projection period: 1 year Return rate for year 1: 0%
Expected output
Projected ending balance: $2,200.00
At a 0% return, the investment earns no growth. The ending balance is the $1,000 initial amount plus 12 monthly contributions of $100: $1,000 + (12 x $100) = $2,200. Checking in reverse, $2,200 - $1,000 = $1,200, which equals 12 contributions.
The projection starts with the initial amount and advances through the selected duration. Monthly contributions increase the balance throughout that duration, while the entered return assumptions determine investment growth. Consequently, later returns can affect both the original principal and amounts added earlier. With a zero return, the result reduces to initial amount plus the total of all monthly contributions.
Variable rates let separate parts of the projection use different expected returns. This can represent an optimistic period followed by a weaker one, or support comparisons between several hypothetical paths. The order matters because each period begins with the balance produced by earlier periods. Equal average rates do not necessarily imply equal ending balances when the rates occur in a different sequence.
No. The ending balance combines the initial investment, all monthly contributions, and growth or loss from the assumed returns. To evaluate growth alone, compare the ending balance with total money contributed. Total contributions equal the initial amount plus the monthly contribution multiplied by the number of contribution months.
No. They describe scenarios supplied by the user, not the sequence the market will deliver. Variable rates are useful for testing sensitivity to stronger and weaker periods, including unfavorable cases. They cannot represent every feature of real investing, such as intra-period volatility, security-specific events, or uncertain future contributions.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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