How compound growth works
Compounding means returns can generate additional returns. In this illustration, the initial amount grows monthly and each contribution begins its own compounding path. Time and consistent contributions can have a large effect, but real investment returns vary and can be negative.
What this calculator assumes
The calculator converts the annual rate into a monthly rate, applies monthly compounding, and assumes contributions occur at the end of each month. It does not include fund expenses, advisory fees, taxes, inflation, contribution limits, changing returns, or withdrawals.
How to interpret the result
Separate the result into money contributed and estimated growth. That distinction prevents compounding from feeling magical: contributions do much of the early work, while time may increase the role of growth later.
Practical next steps
- Test at least three return assumptions rather than anchoring on one.
- Reduce the assumed rate to approximate fees or use a separate fee estimate.
- Compare increasing the monthly contribution with chasing a higher return.
- Review account rules, taxes, diversification, and risk using authoritative sources.
For a second official reference, compare the model with the SEC Investor.gov compound interest calculator.