Investment Calculator
Free investment calculator. Solves for end amount, starting amount, monthly contribution, return rate, or years with inflation-adjusted view and Excel export.
Frequently asked questions
How does an investment calculator work?
An investment calculator projects the future value of an account by compounding a return rate on your balance month by month while adding your recurring contributions. It uses the standard future-value formula FV = PV·(1+r)^n + PMT·((1+r)^n − 1)/r, where PV is your starting amount, PMT is the monthly contribution, r is the monthly return, and n is the number of months.
What return rate should I assume for long-term investing?
A globally diversified stock portfolio has returned about 10% nominal / 7% real (after inflation) historically. Use 6-7% for conservative long-horizon planning, 8-10% for a moderate assumption, and always sanity-check with the inflation-adjusted view — a 10% nominal return with 3% inflation is really a 7% return in purchasing power.
What is the difference between nominal and inflation-adjusted returns?
Nominal returns are the raw dollar values you will see on your account statement. Inflation-adjusted (real) returns re-price those future dollars into today's purchasing power. A $1M portfolio in 30 years at 2.5% inflation is worth about $477k in today's dollars — the real number is what actually matters for retirement planning.
What is compound interest and why does it matter?
Compound interest is interest earned on your principal plus previously earned interest — you earn returns on returns. Over long horizons this becomes the dominant driver of wealth: $500/month at 7% for 30 years grows to about $567k, of which only $180k is contributions and the other $387k is pure compounded growth.
How much should I invest each month to reach $1 million?
It depends on your starting balance, return rate, and horizon. At a 7% return starting from $0, you need about $1,175/month for 20 years, $820/month for 25 years, or $380/month for 40 years. Switch this calculator to "Solve For: Monthly Contribution" and enter your target end amount, horizon, and expected return to get the exact number.
Should I invest a lump sum or dollar-cost average?
Historical data shows lump-sum investing beats dollar-cost averaging about two-thirds of the time in rising markets, because the money spends more time compounded. DCA reduces regret risk and is often better psychologically. This calculator supports both: enter a starting amount for lump sum, or set starting to $0 and use monthly contributions for pure DCA.