Compound Interest Calculator - Monthly Contribution Growth
Enter an initial investment, monthly contribution, annual return, and investment period to estimate future balance and compound interest.
Calculation Results
Final Balance
₩300,850,718
Total Contributions
₩130,000,000
Compound Interest Earned
₩170,850,718
Total Return Rate
131.4%
Rule of 72 Doubling Time
About 10.3 years
Monthly Compound Rate
0.583%
Compound Advantage vs Simple Interest
₩73,200,718
Simple-interest estimate under the same inputs: ₩227,650,000
Annual Asset Growth
What Is Compound Interest?
Compound interest is a method where interest accrues not only on the principal but also on previously earned interest. While simple interest generates the same fixed amount of interest each period, compound interest creates a "snowball effect" where interest earns interest over time. For example, investing 10 million KRW at 7% annually for 20 years with compound interest yields approximately 38.7 million KRW, compared to only 24 million KRW with simple interest.
The key to compound interest is "time." The longer the investment period, the more exponentially the compound effect grows. The well-known "Rule of 72" lets you quickly estimate how long it takes for assets to double — simply divide 72 by the annual return rate. At 7%, your principal doubles in roughly 10.3 years. This calculator computes future asset growth by adding monthly contributions to the initial investment and applying the annual return rate with compounding.
Combining regular periodic investments with compounding maximizes the effect even further. Investing 500,000 KRW per month at 7% annually for 20 years grows a total contribution of 120 million KRW to over 260 million KRW. The earlier you start, the greater the benefit of compounding, so it is important to begin as soon as possible, even with a small amount.
Rule of 72
Approximate time for assets to double = 72 / Annual Return Rate
Annual 3%
24.0년
Annual 5%
14.4년
Annual 7%
10.3년
Annual 10%
7.2년
How to Use This Calculator by Search Intent
Compound interest, recurring investment, and investment return searches use similar inputs, but the interpretation differs. Start with the use case that matches your goal.
Enter initial amount, monthly contribution, annual return, and years to estimate final balance and gains over principal.
For deposit-style interest, set monthly contribution to zero or your actual payment amount, then compare the compound result with the simple-interest estimate.
Use monthly contribution to model dollar-cost averaging and compare 10-year or 20-year outcomes.
Use this for long-term annualized return assumptions, not one-trade buy/sell profit calculations.
For ETF-specific long-term investing, target wealth, and dividend reinvestment, continue with the ETF compound calculator.
How to Use the Compound Calculator
This compound calculator estimates future wealth from four inputs: initial investment, monthly contribution, annual return, and time horizon. It supports KRW and USD, so it can also be used for US ETF planning. The result shows final balance, total principal, compound interest earned, and total return.
The annual growth chart shows how principal and total assets diverge over time. Early on, the gap is small, but the difference widens as gains are reinvested and begin earning additional returns. That is why compound calculations should consider both time and contribution consistency, not just the return rate.
For real planning, compare multiple return assumptions. Instead of relying on one optimistic number, test conservative, balanced, and growth scenarios such as 5%, 7%, and 10%. If you already have a target amount, adjust years and monthly contribution to estimate the savings rate required.
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Compound Calculator FAQ
- What does this compound calculator calculate?
- It estimates future balance, total contributions, compound interest earned, and total return from initial investment, monthly contribution, annual return, and time horizon.
- What is the difference between monthly and annual compounding?
- Annual compounding applies growth once per year, while monthly compounding splits the annual return into monthly periods and reinvests growth more frequently.
- Can I use it for recurring investment plans?
- Yes. Enter a monthly contribution to simulate a recurring investment plan for long-term stock or ETF investing.
- Where can I calculate ETF-specific compounding?
- Use the ETF compound calculator for ETF-focused scenarios such as target wealth, dividend reinvestment, and long-term contribution plans.
Rebalance your portfolio regularly to maximize compound returns
Go to Rebalancing Calculator