Investment Calculator

What is an investment calculator?

An investment calculator estimates how a sum of money could grow over time at a steady rate of return. Enter a starting amount, regular contributions, an expected annual return, and a time period, and it projects a future value. It is for planning only — actual returns vary and are never guaranteed.

It answers questions such as: "What could my savings grow to if I invest a fixed amount every month for twenty years?" It is commonly used for savings goals, education funds, or understanding the long-term effect of consistent contributions.

How it works

The calculator uses the future value of money formula. It treats your investment as two parts: the starting amount, which compounds on its own, and your regular contributions, which each compound for the time they remain invested.

Future value = P(1 + r)^t + PMT × (((1 + r)^t − 1) / r), where P is the initial amount, PMT is the regular contribution, r is the rate per period, and t is the number of periods. For monthly contributions, the annual rate is divided by twelve and the years multiplied by twelve to get the monthly rate and number of periods.

The two most important drivers are the rate of return and the number of periods. Because growth compounds — each period's gains earn returns themselves — time matters enormously. Contributions made early have more time to compound, so starting earlier can matter more than investing larger amounts later.

How to use this calculator

1. Enter the initial investment amount — the lump sum you are starting with.
2. Enter the regular contribution — how much you will add each month or year.
3. Enter the expected annual return as a percentage, and note that any figure you use is an assumption, not a promise.
4. Enter the number of years you plan to keep investing.
5. Read the projected future value, along with the breakdown of your total contributions versus the growth on top of them.

Worked example

In this example, suppose someone starts with $10,000, adds $200 every month, and assumes a 7% annual return (assumed for illustration only) over 20 years.

With monthly compounding, the rate per period is 0.07 ÷ 12 and the number of periods is 240. The $10,000 starting amount grows on its own, and each $200 monthly contribution compounds for the months it is invested. The projected future value is approximately $144,573.

Total contributions are $58,000 ($10,000 plus $200 × 240 months); the remaining ~$86,573 is growth from compounding. The longer money stays invested, the larger the share of the final balance that comes from growth rather than contributions. Remember the 7% return is assumed for illustration; real returns fluctuate and can be lower or negative in some years.

Tips and limitations

• Try several return assumptions — for example 5%, 7%, and 9% — to see how sensitive the result is to the rate.
• Lengthen the time horizon to see the effect of starting earlier; even five extra years can change the result substantially.
• Regular contributions often matter more than the starting amount over long periods, because small consistent additions add up through compounding.
• It does not cover inflation: $144,573 in twenty years will buy less than the same amount buys today.
• It does not include taxes, fees, or trading costs, all of which reduce real returns.
• It assumes a constant rate of return, which no real investment delivers. Treat every result as a rough illustration, not a forecast.