Compound Interest
Compound-Interest Assumptions and Investment Limits
Reference date and last reviewed: July 11, 2026
Calculation Basis
Projects a future amount from initial money, recurring contributions, an estimated annual return, compounding frequency, and time, assuming the entered return continues.
Reference Limits
The entered return is not guaranteed, and the estimate does not model taxes, fees, inflation, currency changes, loss periods, or the exact timing of contributions. It is not an investment or principal guarantee.
When to Confirm Officially
Before making an investment or long-term funding decision, review the product's risk, fee, and tax disclosures together with your time horizon and ability to tolerate losses.
Usage Tips
Separate your starting principal and regular contributions when planning long-term growth
Compound growth can change a lot depending not only on the return rate, but also on the investment period and the amount you add each month. Enter your starting principal, monthly contribution, expected annual return, and time period to compare the share of principal and earnings, year-by-year asset growth, and long-term saving or investing plans.
What is Compound Interest?
The Compound Interest Calculator is a robust financial forecasting utility that projects the future value of investments based on initial principal, recurring monthly contributions, estimated annual return rates, investment duration, and compounding frequencies. It simulates the compounding effectโwhere interest earned generates additional interest over timeโenabling users to compare daily, monthly, or annual compounding models to optimize wealth-building strategies for retirement, college funds, or dividend reinvestment plans.
How to Use
- 1Enter your initial deposit or starting investment principal.
- 2Input the recurring contribution amount and select the deposit frequency (e.g., monthly, annually). If none, enter 0.
- 3Specify the expected annual interest rate (%) and choose your compounding frequency (annually, monthly, quarterly, daily).
- 4Enter the total investment time horizon in years or months.
- 5Review the calculated future value, total cumulative principal, total interest earned, and examine the asset growth trajectory over the designated timeline.
Separate deposited principal from simulated growth
Last reviewed: July 11, 2026Monthly compounding with contributions
next balance = current balance ร (1 + annual rate รท 12) + monthly contribution
The calculator updates the balance once per month, adds the monthly contribution at the end of that cycle, and reports total contributions separately from the balance above them.
KRW 1,000,000 plus KRW 100,000 monthly for three years
- โข Initial principal KRW 1,000,000
- โข Monthly contribution KRW 100,000 at an assumed 6% annual rate
- โข Three-year term with monthly updates
- 1. Total contributions = 1,000,000 + 100,000 ร 36 = KRW 4,600,000
- 2. Monthly rate = 6% รท 12 = 0.5%
- 3. Apply 0.5% to the balance and add the contribution for 36 cycles
The projected balance is about KRW 4,641,484, including KRW 4,600,000 contributed and about KRW 41,484 in simulated interest.
How to read the result
- Do not treat the entire final balance as profit; separate contributions from simulated interest.
- Even at the same rate, term length and contribution timing change how long each deposit compounds.
Conditions that change the result
- The rate is assumed to be constant and does not guarantee market returns or principal.
- Taxes, fees, inflation, and beginning-versus-end-of-month deposits are not included in the basic result.
Common input mistakes
- Enter 6 as the user-facing annual rate; the calculator converts it to a monthly decimal internally.
- Recording the entire final balance as investment profit confuses principal with interest.
Reference Knowledge
- โStandard Compound Interest Formula: A = P ร (1 + r/n)^(nรt), where A is future value, P is principal, r is annual interest rate, n is compounding periods per year, and t is time in years.
- โFuture Value of an Annuity (with contributions): Uses the combined annuity formula to account for recurring additions growing alongside the starting base.
- โCompounding Frequency Factor: With the same nominal annual yield, more frequent compounding (monthly or daily vs. annually) triggers faster reinvestment of interest, accelerating the growth rate of the portfolio.
- โRule of 72: A quick mental math shortcut to estimate how long it takes for an investment to double in value under compound interest. The formula is 72 / Annual Interest Rate. For instance, at a 6% annual return, your money will double in approximately 12 years.
FAQ
Q.What is the fundamental difference between simple and compound interest?
Simple interest is calculated only on the initial principal amount. Compound interest, however, is calculated on the principal plus all of the accumulated interest from previous periods. Over time, compound interest creates exponential growth, widening the gap between the two methods.
Q.Are inflation and investment taxes automatically subtracted from the total?
No. This calculator computes nominal future values based purely on mathematical compound interest models. To estimate your real purchasing power or net returns, you should manually subtract local tax rates (like capital gains tax) and average inflation expectations from the final projected balance.
Q.What happens if I enter a negative annual return rate?
Entering a negative rate simulates reverse compounding, projecting how your capital will decay over time. This is useful for evaluating worst-case market scenarios, portfolio drawdown impacts, or purchasing power decay under high inflation.
Q.Are recurring contributions assumed to be made at the beginning or end of each period?
The calculator follows the standard end-of-period (ordinary annuity) convention, where contributions are deposited at the end of each billing cycle and start earning interest from the following period.
Q.How can I use this to simulate Dividend Reinvestment Plans (DRIP)?
Input your estimated dividend yield as the annual interest rate, set the compounding frequency to match the payout cadence (e.g., quarterly or monthly), and run the projection. This provides a clear roadmap of how your holdings grow when all dividends are systematically reinvested.
