Use this compound interest calculator to explore how money can grow when returns are earned on both your original amount and any previously generated returns. It helps you compare different starting amounts, regular contributions, time periods and assumed rates of return. The illustration is educational only and is not financial advice. Investments can fall as well as rise, past performance is not a guide to future results and capital is at risk. Results are estimates that may differ from real outcomes once fees, taxes, inflation and market movements are taken into account.
What this calculator assumes
- Returns are assumed rather than guaranteed and may vary materially in reality.
- Contributions are made at the frequency and timing selected in the calculator.
- Fees, taxes and inflation are estimates only unless explicitly entered.
- Capital is at risk and the value of investments can go down as well as up.
How compounding works
Compounding means returns are added to your balance and may then go on to generate further returns themselves. Over time this can create a snowball effect, especially when money is left to grow for longer periods. The calculator shows how an initial amount may change across a chosen number of years using the rate you enter. In practice, actual growth is rarely smooth. Markets move up and down and returns vary from year to year, so this is a way to understand the mechanics rather than a forecast.
Adding regular contributions
Regular contributions increase the amount exposed to future returns and can materially change the final estimate over time. This is useful for comparing scenarios with and without monthly investing, especially if you are trying to understand why consistency matters. The result still depends on the assumptions entered, including the timing and size of contributions. Small changes to the contribution amount, contribution increases or time period can lead to noticeably different outputs, particularly over longer horizons.
Assumptions, fees and inflation
The assumed return is an illustration, not a promise. Real investments usually involve costs such as fund fees, platform fees or dealing costs and those can reduce the outcome. Inflation also matters because a future balance may not have the same spending power as the same number today. The calculator can show an inflation-adjusted estimate, but this still depends on the rate you choose. Treat the output as a planning prompt, not a prediction.
Useful official sources
FAQs
What does compound interest mean in this calculator?
It shows the effect of returns being earned on both the original amount and on any returns already added to the balance. It is an educational illustration of how growth can build over time.
Can I include regular contributions?
Yes. You can add monthly contributions and an optional annual contribution increase to see how regular investing changes the estimate.
Why does the result change so much over longer periods?
Longer periods give compounding more time to work, but they also magnify assumptions. Small changes in return, fees or contributions can create large differences over decades.
Is this a prediction of future performance?
No. It is an estimate for educational purposes only. Actual outcomes can differ because of fees, taxes, inflation, market movements and the risk that investments may fall in value.