Compound Interest Calculator
Use our free compound interest calculator to forecast the exponential growth of your investments over time with initial deposits, regular monthly contributions, and flexible compounding frequencies.
Principal vs. Interest Breakdown
Asset CompositionBalance Growth Timeline
Green = Balance, Blue = ContributionsYear-by-Year Projection
| Year | Starting Balance | Annual Deposits | Interest Earned | Total Contributed | Ending Balance |
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The Power of Compound Growth
Compound interest occurs when earnings on an investment are reinvested to generate additional returns in subsequent cycles. Unlike simple interest, which only pays returns on the original principal, compound interest causes wealth to grow at an accelerating rate over time.
Concrete Compounding Example
Consider an investor who starts with $10,000 and invests an additional $500 per month into a diversified S&P 500 index fund averaging an annualized return of 7.00% compounded monthly.
- After 10 Years: Total contributions equal $70,000, yet the account balance is approximately $106,752 ($36,752 in pure interest).
- After 20 Years: Total contributions reach $130,000, but compound interest elevates the portfolio to $301,424—meaning interest accounts for over 56% of total wealth.
- After 30 Years: Total contributions total $190,000, while the portfolio balance crosses $686,639, generating nearly half a million dollars in pure growth.
Factors Influencing Compound Interest
Three critical variables determine your ultimate investment results:
- Time Horizon: The single greatest catalyst for compound growth is time. An extra 10 years in the market often produces more dollar growth than doubling your monthly savings rate later in life.
- Rate of Return: A difference of 2% in annual returns (e.g., 6% vs. 8%) can alter a 30-year retirement nest egg by hundreds of thousands of dollars.
- Consistency of Deposits: Dollar-cost averaging via regular monthly contributions ensures you buy shares at various market levels, smoothing volatility while steadily increasing the earning base.