Compound interest calculator
Calculate the expected balance and annual balance using the initial amount, monthly deposits, and assumed annual return.
Input
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Result
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The annual return rate is a user‑defined assumption and is not a guaranteed rate. Interest and returns are reinvested monthly and paid at the end of the month. Taxes·fees·inflation·financial institution days·unit conversion are not considered.
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Calculation·conversion criteria
Divide the expected balance and principal by the user’s assumed annual return based on the initial amount and monthly end-of-month deposits.
Input example
Initial 1,000,000 won · 100,000 won per month · 5% annual return · 10 years
Assuming an initial 1,000,000 won is added by 100,000 won at the end of each month, and the effective annual return remains at 5% for 10 years, the expected balance is 17,065,211 won. The total deposit is 13,000,000 won, and the difference of 4,065,211 won is due to the assumption. Interest is calculated by reinvesting monthly.
How to use
- Use the provided example value or change the initial amount (won), monthly payment (won), annual return rate (%), and duration (years) items.
- Click Verify result and check the following result.
- Result can be copied if needed.
Frequently Asked Questions
Is the annual return a fixed interest rate?
No. It is a hypothetical effective return rate entered by the user for comparison. It does not refer to actual deposit rates, investment returns, or principal preservation.
When is the monthly payment amount updated?
Assume that after updating the monthly interest, the payment amount is added at the end of the month. The timing of payments during the month or the number of days per financial institution is not considered.
Will taxes and fees also be calculated?
No. It is a simple estimate excluding taxes, fees, inflation, and return variations. Interest and returns are calculated as ongoing investments.
Calculation criteria and reference materials
- Investor.gov — compound calculator
Range of a public calculator that inputs initial amount, monthly payment, duration, and user‑assumed return rate. This tool specifies its own monthly conversion assumption for effective annual return rates.
Verification of calculation criteria: · Calculation·verification principles · Report errors