Investment Calculator
Project the future value of your investments with an initial amount, monthly contributions, expected return and time.
Investment Calculator — input your values
What does this financial calculator do?
This investment calculator projects how a portfolio grows when you invest an initial lump sum and then add regular monthly contributions. It applies your expected annual return with monthly compounding and shows the final value after the time you choose.
The breakdown splits the result into the money you contributed yourself and the earnings generated by the market. A year-by-year chart shows how earnings accelerate over time — the core reason long-term investing works.
Formula and variables
The model compounds monthly and reinvests all returns, which is how most brokerage accounts work.
| Symbol | Meaning |
|---|---|
| FV | Future value |
| P | Initial investment |
| r | Monthly return (annual return ÷ 12) |
| t | Number of monthly periods |
| C | Monthly contribution |
Worked example
You invest $10,000 today, add $500 per month, and earn an average 7% per year for 20 years.
- Monthly rate: 7% ÷ 12 = 0.5833%.
- Total contributed: $10,000 + ($500 × 240) = $130,000.
- After 240 months of compounding, the portfolio reaches ≈ $279,100.
- Earnings: $279,100 − $130,000 = ≈ $149,100.
Answer: Final portfolio value ≈ $279,100, with roughly $149,100 of growth on $130,000 contributed.
Tips and common mistakes
Tips
- Consistency beats timing: regular monthly contributions smooth out market ups and downs.
- Keep fees low — a 1% annual fee can consume a large share of long-run returns.
- Reinvest dividends rather than spending them to keep compounding at full power.
- Review your asset allocation as retirement nears; a lower-risk mix protects the balance you have built.
Common mistakes to avoid
- Using an optimistic 10%+ return for conservative planning — use 6% to 8% and be pleasantly surprised.
- Ignoring fees and taxes, which quietly reduce the effective return year after year.
- Forgetting to increase contributions as your income grows over the decades.
Investment Calculator — frequently asked questions
What return should I assume?
The long-run average for global stock markets is roughly 7% to 8% per year before inflation (about 4% to 5% after). For conservative planning, use 5% to 6%.
How do monthly contributions help?
They add new money that compounds too, and they automate the habit — most of a long-term portfolio's balance comes from contributions plus their growth.
Does this calculator account for inflation?
No. If you use a rate around 4% to 5% you are effectively projecting in today's dollars; if you use 7% to 8%, the result is in future dollars that buy less.
What is dollar-cost averaging?
Investing a fixed amount at regular intervals means you buy more shares when prices are low and fewer when high, smoothing your average cost over time.
Can I use this for a retirement account?
Yes — 401(k)s and IRAs work exactly this way. Use your real contribution rate and remember the results grow tax-free or tax-deferred inside those accounts.
Why does the growth chart accelerate so sharply?
Compounding — earnings from early years stay invested and earn more in later years, so the balance grows exponentially instead of in a straight line.