Albert Einstein reportedly called compound interest the eighth wonder of the world. Whether he said it or not, the math is staggering. Small, regular investments can grow into life-changing wealth — but only if you give them enough years to compound.
Our investment growth calculator shows you three scenarios: expected, optimistic, and pessimistic. Here's what the numbers mean for your portfolio and how you can use them to plan smarter.
How does the investment growth formula work?
The future value formula combines two things: the growth of your starting lump sum and the growth of your ongoing contributions. Both compound monthly at your expected rate of return.
Even if you start with **$0**, regular contributions of **$500/month** at **8%** return grow to over **$290,000** in 20 years. That's only **$120,000** in contributions — the other **$170,000+** comes from market returns.
Why do you need three return scenarios?
No investment returns exactly the same amount every year. Some years you'll see **20%** gains. Others you'll see **-10%** losses.
Our calculator shows expected, optimistic (rate + variance), and pessimistic (rate - variance) scenarios.
A **plus or minus 2%** variance is reasonable for a diversified portfolio. The range of outcomes helps you plan conservatively while understanding the upside potential.
Use the pessimistic scenario for planning purposes and the optimistic scenario for motivation. Your actual results will likely fall somewhere in between — and that's exactly why you need both numbers.
Model Your Investment Growth
Enter your starting amount, regular contribution, time horizon, and expected return to see three scenarios. Our calculator shows your expected, optimistic, and pessimistic outcomes so you can plan with confidence.