Investment Growth Calculator
Free Compound Interest Calculator
See how your investments grow with compound interest over time. Enter your starting amount, regular contributions, and expected return rate to project your portfolio's future value. This compound interest calculator uses the formula A = P(1 + r/n)nt to show how reinvested earnings accelerate growth, turning consistent contributions into long-term wealth.
Starting with $10,000 and adding $500 per month at a 10% annual return for 20 years, you'd contribute a total of $130,000 — and your investment would grow to approximately $452,965 thanks to compound interest. That's $322,965 in pure growth.
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Frequently Asked Questions
Key concepts for long-term wealth building
How does compound interest work?
Compound interest means you earn returns not just on your original investment, but also on all the returns that have already accumulated. In year one, $10,000 at 10% earns $1,000. In year two, you earn 10% on $11,000 — that's $1,100. Each year, the growth accelerates.
Albert Einstein reportedly called compound interest 'the eighth wonder of the world.' The key factor is time — $10,000 growing at 10% becomes $67,275 after 20 years and $174,494 after 30 years. Starting just 10 years earlier nearly triples your money.
How much difference do regular contributions make?
Regular contributions dramatically amplify compound interest. A one-time $10,000 investment at 10% grows to $67,275 in 20 years. But adding just $200 per month to that same investment turns it into $210,037 — more than three times as much.
The key is consistency. Even small monthly contributions create a powerful snowball effect because each deposit starts compounding immediately. A $200 monthly contribution over 30 years at 10% turns $72,000 in deposits into over $450,000 — that's the difference between saving and investing.
What is the Rule of 72?
The Rule of 72 is a shortcut to estimate how long it takes for an investment to double. Divide 72 by the annual return rate — at 8% growth, your money doubles in approximately 9 years. At 12%, it doubles in about 6 years.
This quick mental math helps you set realistic expectations. If the S&P 500 averages ~10% per year, your money doubles roughly every 7.2 years. Try our dedicated Rule of 72 Calculator for instant doubling-time estimates.
What return rate should I expect?
Historically, the S&P 500 has returned approximately 10% per year before inflation (about 7% after inflation). However, annual returns vary wildly — from -37% (2008) to +32% (2013). The 10% average only materializes over long time horizons.
For conservative planning, use 7% (inflation-adjusted). For nominal projections, 10% is reasonable. Bonds typically return 4-6%. Higher expected returns always come with higher risk — there are no guaranteed high returns.
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For informational and educational purposes only — not investment advice.