Enter a starting amount, a monthly contribution, and an expected return. The calculator compounds it period by period and shows how much of the final balance came from you — and how much came from growth.
Each compounding period, the balance grows by the annual rate divided by the number of periods, then your contribution is added. Contributions are assumed at the end of each month. The formula is the standard future-value-of-an-annuity calculation — no fees, taxes, or inflation are included, so treat the result as a before-cost illustration.
Use the expected annualized return after fees. A diversified stock portfolio has historically returned around 7% per year after inflation over long periods — many planners use 6–8% nominal for equities and 2–4% for bonds or savings. Pick a rate below your hopes, not above them.
Barely. Monthly vs. annual compounding on the same nominal rate changes the outcome by a fraction of a percent over decades. What matters far more is the rate itself, how much you contribute, and how long you leave it alone.
Compounding is exponential: each year's gains earn their own gains the next year. Early on, your contributions are most of the balance. Later, the balance is large enough that even a modest rate adds more dollars per year than you contribute. Starting early beats contributing more later — time is the input you can't buy back.
Yes — the 401(k) calculator uses the same compounding engine, then layers on salary-based contributions, employer match, plan fees, and inflation. Use this page for the general concept; use that one for retirement planning.
Illustration only — not financial advice. Actual investment returns vary and can be negative; fees, taxes, and inflation are not included. Past performance does not predict future results.