Everything About Compound Interest
Compound interest — famously called the eighth wonder of the world — makes wealth grow exponentially because interest earns interest. 10M KRW at 7% per year becomes about 19.67M in 10 years, 38.7M in 20, and 76.1M in 30. This calculator takes both a lump sum and a monthly deposit and instantly computes the final amount under annual or monthly compounding.
Monthly deposit investing is the most practical way to build assets without a large lump sum. Saving 500K KRW every month at 5% with monthly compounding for 20 years turns 120M of contributions into about 205.5M — over 85M of interest. The year-by-year table splits cumulative principal from cumulative interest, so you can watch the interest share catch up to the principal over time.
The Rule of 72 is the most famous shortcut for gauging compounding speed: divide 72 by the annual return to get the doubling time. At 4% it takes 18 years, at 6% 12 years, at 8% just 9 years. It shows intuitively how seemingly small rate differences create huge long-term gaps, and the calculator displays the doubling time for your rate automatically.
Pro tip: the three levers of compounding are time, rate, and consistency. Starting 10 years earlier often beats squeezing out a few extra percentage points, and reinvesting instead of withdrawing is the key. Note that this is a simulation that excludes taxes (Korean 15.4% interest income tax) and fees; real returns fluctuate and are never guaranteed. This calculator is for information only and is not investment advice.