Compound Growth With Monthly Investing Calculator
Project what a starting balance plus a fixed monthly investment grows to, and see how much of the ending pot is contributions versus compounded growth.
How it works
FV = P(1+i)ⁿ + PMT·[((1+i)ⁿ − 1) ÷ i] · i = annual return ÷ 12 · n = years × 12
A lump sum compounds on its own while every monthly deposit starts its own compounding clock, so the earliest contributions do the heaviest lifting. Because the return is applied to a balance that both grows and receives fresh money, the ending pot separates into two parts: the cash you contributed and the growth the market added on top. Over long horizons the growth share usually overtakes the contributions — that crossover is the whole point of investing early.
Worked example
Start with $10,000, add $500 a month, earn 8% compounded monthly for 20 years. The monthly rate is 0.667% over 240 months, giving about $343,000. You contributed $130,000, so roughly $213,000 — over 60% of the pot — is pure compounded growth.
Frequently asked questions
Why compound monthly instead of yearly?
Because you invest monthly, each deposit should start earning immediately rather than waiting for a year-end. Monthly compounding matches how contributions actually accrue and gives a slightly higher, more realistic figure than annual compounding of the same rate.
Is the return guaranteed?
No. The rate you enter is an assumption. Real markets swing year to year, and the order of good and bad years matters, especially near the end. Treat the result as a smooth projection, not a promise.
How is this different from a plain CAGR?
A CAGR describes one sum growing from a single start to a single end. Here money flows in every month, so no single growth rate applies to the whole thing — the money multiple (ending ÷ contributed) is the closest simple summary.
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Educational estimate, not investment advice. Markets involve risk of loss and future returns are never guaranteed.