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How do I calculate how much my investment will grow with monthly contributions?

Short answer

Investment growth combines your starting balance, regular contributions and compounding returns. Because each contribution also starts earning, the total grows faster than contributions alone. A free investment calculator runs the future-value math in your browser for any starting amount, monthly contribution, rate and time.

Two engines: the lump sum and the contributions

The final balance has two parts. Your starting amount grows by compound interest, using A = P x (1 + r/n)^(n x t). Your regular contributions grow too, but each one compounds for less time than the one before it, so the calculator sums a future value across every contribution. Adding both parts gives the projected balance. Any rate you enter is an assumption, not a guaranteed return.

Time does the heavy lifting

Because contributions made early compound for the longest, starting sooner matters more than contributing more later. Two people who invest the same total end up far apart if one started years earlier. The calculator makes this vivid: extend the number of years and watch how much of the final balance is growth rather than the money you put in.

Frequently asked questions

Does the calculator guarantee a return?

No. It projects growth from the rate you enter, which is an assumption. Real investment returns vary and can be negative.

Why do early contributions matter more?

They compound for more years. A dollar invested early earns returns on returns for longer than the same dollar invested later.

What inputs do I need?

A starting balance, a monthly or yearly contribution, an assumed annual return, and the number of years.

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