The Magic of Compound Interest
Compound interest is the interest on a loan or deposit calculated based on both the initial principal and the accumulated interest from previous periods. The longer the period, the more the interest-on-interest effect grows, so time often matters as much as the rate.
Unlike simple interest, which only applies to the principal, compound interest reinvests your earnings. This creates a "snowball effect" where your wealth grows slowly at first but accelerates rapidly as the interest itself starts earning more interest.
How to Use Each Mode
Our calculator offers three specialized modes to fit your investment strategy.
Ideal for one-time investments. Calculate how a single deposit grows over time with various compounding frequencies.
Designed for regular saving habits. Factor in an initial deposit plus monthly contributions to see your long-term wealth building progress.
Goal-oriented planning. Determine how much time or what interest rate is required to reach your financial milestones.
The Power of Compounding Frequency
The frequency with which interest is compounded affects the final amount. The more often interest is added to the principal, the faster the balance grows.
- Yearly: Interest is added once a year. Common for fixed deposits.
- Quarterly: Every 3 months. Useful for dividend-paying stocks.
- Monthly: Every month. The most common standard for regular savings.
- Daily: Every day. The most powerful effect, often seen in crypto staking.
Mathematical Formulas
Standard financial formulas used in this calculator.
Standard Compound
A: Final Value, P: Principal, r: Annual Rate, n: Freq, t: Years
Savings Accumulation
PMT: Regular Payment. The second term represents the future value of the annuity.
Target Time (Logarithm)
Calculates the required time (t) using log functions based on target (A) and initial (P).
3 Tips for Wealth Growth
Consistency and time are more important than chasing high-risk short-term gains. The longer you stay in the market, the stronger the magic.
A dollar tomorrow is worth less than a dollar today. Aim for targets that account for a 2-3% annual inflation rate.
Estimated time to double your money = 72 divided by the growth rate. (e.g., 6% growth doubles in 12 years).
Using Compound Interest Results for Planning
Compound interest earns interest on interest, so the gap with simple interest widens over time. Results assume a constant rate; taxes, fees and rate changes affect real returns.
Worked example: KRW 10 million at 4% a year for 10 years
- Simple interest: 10,000,000 × 4% × 10 = 4,000,000 → 14,000,000
- Annual compounding: 10,000,000 × 1.04¹⁰ ≈ 14,802,000
- The difference of about 802,000 is interest earned on interest.
Over 20 years the compound result grows to about 21.9 million versus 18 million with simple interest. In Korea, deposit interest is usually taxed at 15.4%.
Before you rely on the result
- Do not confuse annual and monthly rates.
- Account for taxes and fees separately.
- Treat high return assumptions as optimistic scenarios.
- This calculator is not investment advice. Products with principal risk need separate review.
Frequently asked questions
Is a shorter compounding period always better?
With the same nominal rate it usually is, but taxes, fees and withdrawal conditions can matter more.
What is the Rule of 72?
Divide 72 by the annual rate to estimate the years needed to double. At 4% that is about 18 years.