How monthly savings interest is calculated
The first deposit is made when the account opens, followed by equal monthly payments. For a 12-month plan, the first payment earns 12 months of interest and the last earns one month. This differs from the month-end contributions used in the investment compound calculator.
Simple interest before tax = M × n(n+1) ÷ 2 × annual rate ÷ 12
Monthly compounding: add the deposit at the start of each month, then apply the monthly rate
Example: KRW 500,000 monthly, 3.5% a year, 12 months, simple interest
Principal is KRW 6,000,000 and interest before tax is KRW 113,750. Estimated standard tax is about KRW 17,518, giving about KRW 6,096,233 at maturity. Rounding each displayed amount to whole won can create a KRW 1 difference between components and totals.
Why the entire principal does not earn a full year of interest
Even with total deposits of KRW 6,000,000, each payment is invested for a different time. This cannot be compared directly with depositing KRW 6,000,000 upfront at the same annual rate. Flexible payments, late payments and special payment schedules require separate calculations.
Simple interest and monthly compounding
Simple interest applies only to the deposited principal. Monthly compounding adds earned interest to the balance for the next month. The annual rate is treated as nominal and divided by 12. Products with daily or annual compounding may give different results.
Standard tax and tax exemption
Standard withholding is estimated at 15.4%: 14% interest income tax plus 1.4% local income tax under Korean rules. Tax exemption assumes you meet the relevant eligibility and limits. Selecting it does not make an ordinary product exempt. Any final comprehensive financial income tax is separate.
Why actual maturity proceeds may differ
These estimates use whole months and a constant rate. Actual days, payment dates, early withdrawal, bonus-rate conditions, tax truncation, small-tax exemptions and product-specific terms are excluded. Interest is assumed to be taxed once at maturity; displayed amounts are rounded to whole won. Check the institution's terms and settlement figures.