Free investment growth calculator

How the investment growth calculator works

This calculator projects what an investment could become by compounding it month by month. It starts with your initial amount, adds your monthly contribution, and grows the whole balance at the annual return you choose — then repeats that for every month of your time horizon. Because each month’s growth is calculated on the new, larger balance, returns build on returns. The result is the classic hockey-stick curve you see in the chart: for the first several years your balance is mostly the money you put in, but given enough time the growth overtakes your contributions and becomes the largest part of your wealth.

Why time matters more than amount

The single biggest lever in investing isn’t how much you invest — it’s how long it compounds. A dollar invested at 25 has roughly four decades to double and redouble before a typical retirement; the same dollar invested at 45 has half as long and ends up worth a fraction as much. That’s why financial planners push people to start early even with small amounts. Try it yourself: add ten years to the horizon and watch the final balance jump far more than a similar increase to your monthly contribution would. Starting now, imperfectly, beats waiting for the “right” amount.

How to use it

Enter your starting amount (use 0 if you’re beginning from scratch), the amount you can invest each month, an expected annual return, and the number of years you’ll stay invested. The headline shows your projected balance, the bars split it into what you contributed versus what growth added, and the chart traces both lines over time so you can see the gap widen. Adjust the return rate to model an optimistic and a conservative scenario — the honest way to use any projection is as a range, not a single promised number.

A worked example

Start with $5,000, add $500 a month, and assume a 7% annual return for 30 years. You would personally contribute $185,000 over that period — but the projected balance is far larger, because roughly three decades of compounding more than doubles your money on top of what you put in. Shorten the horizon to 20 years and the ending balance falls sharply, even though you only invested ten fewer years. That sensitivity to time is the whole point: it’s the clearest argument there is for starting today.

Where to put the money

A projection is only useful if you actually invest. For most people the order is: capture any employer 401(k) match first (it’s free money), then fund tax-advantaged accounts like an IRA, then a regular brokerage account for anything beyond that. Low-cost, broadly diversified index funds are the standard core holding, because fees compound against you the same way returns compound for you. To see how this plays out specifically for retirement, switch to the retirement calculator.

Related tools and guides

Plan the long game with the retirement calculator, see how inflation erodes idle cash with the inflation calculator, or compare safe places for shorter-term money with where to park cash. New to it all? Read our guide on getting started in investing. This page is for general information and is not financial advice.