Compound Investment Calculator
Calculate the future value of regular monthly investments with compound interest. Visualize the growth of your principal vs. returns over time. Free online calculator.
Final portfolio value
¥12,331,010
Total contributions
¥7,200,000
Investment gains
+¥5,131,010
(+71.3%)
Portfolio growth
* This calculator uses compound interest formulas for estimation only. Actual results may differ due to fees, taxes, and market fluctuations. This is not financial advice.
How to Use
Set your contribution amounts
Enter your monthly contribution amount and any initial lump sum you plan to invest. Use the sliders or type directly.
Set the return rate and period
Enter your expected annual return rate. A common benchmark for index funds is 5–7% per year. Set the number of years you plan to invest.
Read the results
The summary cards show your final value, total contributions, and total gains. The bar chart shows year-by-year growth — blue is principal, green is returns.
FAQ
- Long-term average annual returns for broad index funds (global equities, S&P 500) have historically been around 5–7% per year. Use 3–4% for conservative estimates, 7% for optimistic scenarios. Past performance does not guarantee future results.
- Compound interest means you earn returns not just on your original principal, but also on all previously earned returns. For example, ¥1,000,000 at 5% annually becomes ¥1,050,000 after year 1, then ¥1,102,500 after year 2. The longer you invest, the more powerful this 'snowball' effect becomes.
- No. This calculator does not account for management fees (typically 0.1–1% per year for index funds) or capital gains taxes. In practice, subtract estimated fees from your expected return rate, and factor in applicable taxes on withdrawals.
- A lump sum is invested all at once and grows immediately with compound interest. Monthly contributions (dollar-cost averaging) are added regularly over time, so earlier contributions grow longer. Combining both — a lump sum plus monthly contributions — generally produces the best results.