Investment Calculator

How to use this investment calculator

Enter your initial investment — the lump sum you are putting in today. Add a monthly contribution if you plan to keep investing each month, set an expected annual return, and choose how many years you will stay invested. The calculator projects your future value, totals up everything you contributed, and shows your total return and return on investment (ROI). Adjust the sliders to compare scenarios instantly.

How this is calculated

We grow your balance month by month. Each month we apply one-twelfth of your annual return to the running balance and then add your monthly contribution. After all the months have run, that ending balance is your future value. Your total invested is the initial amount plus every monthly contribution. The total return is future value minus total invested, and ROI is that return divided by what you put in, expressed as a percent. Returns are assumed constant for simplicity — real markets rise and fall, so treat this as a long-run estimate.

Educational estimate, not investment advice — see our disclaimer.

A worked example

Suppose you start with $10,000 and add $300 every month for 20 years at a 7% annual return. Over those two decades you contribute $10,000 up front plus $72,000 in monthly deposits, for $82,000 of your own money. With monthly compounding the balance often grows to roughly $197,000, which means about $115,000 came from investment growth rather than your deposits. That works out to an ROI of around 140% — your money has more than doubled on top of being returned.

Future value vs. ROI

These two numbers answer different questions. Future value tells you how much your account is worth at the end — the dollar figure you can spend or reinvest. ROI tells you how efficiently your money worked: it strips out the size of your contributions and expresses the gain as a percentage of what you put in. A small account with a high ROI may have grown faster in percentage terms than a large account with a low ROI, even if the large account holds more dollars. Looking at both keeps you honest about whether a higher balance came from saving more or from earning more.

Returns are not guaranteed

The expected return you enter is an assumption, not a promise. Historically the broad US stock market has returned roughly 7% per year after inflation over the long run, but individual years swing widely — some sharply up, some down. Sequence of returns, fees, and taxes all change the real outcome. Use a conservative figure for planning and revisit your numbers as conditions change. For comparison you can model pure interest growth with our compound interest calculator, or map out a path to financial independence with the FIRE calculator.

Tips to improve your results

• Start early — the longest dollars compound the most, so time in the market beats timing the market.
• Automate contributions — steady monthly deposits add fuel that growth then multiplies.
• Mind the fees — even a one percent expense ratio quietly subtracts from your return every year.
• Use tax-advantaged accounts — sheltering gains from tax lets more of your return keep compounding.