Compound Interest Simulator
About this tool
Shows how an initial amount plus monthly contributions grows each year at a fixed annual return, compounded monthly: each month the balance earns the annual rate ÷ 12, then the contribution is added.
Investing 1,000,000 won a month at 7% for 10 years turns 120,000,000 won into about 173,080,000 won; over 20 years, 240,000,000 won becomes about 520,930,000 won. Doubling the time more than doubles the gain — that is compounding.
Returns are assumed constant, with no tax, fees or inflation. Real returns vary year to year, so use it to estimate long-term averages.
FAQ
What is the rule of 72?
72 ÷ annual return ≈ years to double. At 7%, about 10 years.
Is tax included?
No. Results are before tax.
Negative returns?
Enter a negative rate such as -5.