Why do deposits and monthly savings earn different interest?
Compare payment timing, after-tax interest and compounding on consistent terms.
Deposits invest a lump sum; monthly savings invest gradually
A lump-sum deposit stays invested for the whole term, while each payment into a regular savings plan has a different investment period. That is why identical headline annual rates and total deposits can produce different interest. Compare the timing and amount of payments first.
KRW 6 million upfront versus monthly installments
Assume 3.5% annually for 12 months, simple interest before tax. Depositing KRW 6 million upfront earns KRW 210,000. Paying KRW 500,000 at each month-start earns KRW 113,750, because payments earn interest for 12 down to one month. This alone does not make monthly savings inferior: some payments use future income not available upfront.
Compare after-tax proceeds, not just headline rates
Assuming standard Korean interest withholding of 15.4%, the deposit's KRW 210,000 interest becomes KRW 177,660 after tax. The monthly plan's KRW 113,750 becomes about KRW 96,233. Tax exemption requires eligibility and limits; any final comprehensive financial income tax is outside this estimate.
Separate compounding from bonus-rate conditions
Monthly compounding adds earned interest to the next month's balance; it does not automatically qualify you for a promotional rate. Check salary-transfer, card-spending or automatic-payment conditions, eligible balances and early-withdrawal rates in the product documents. Actual days, payment dates and rounding may differ from the calculator.
Make comparisons using consistent assumptions
Use the deposit calculator for money you already hold and the monthly savings calculator for future recurring payments. Align term, annual rate, interest method and tax treatment, then compare principal separately from net interest. Verify deposit-protection eligibility and limits using the product documents and current Korea Deposit Insurance Corporation guidance.
Sources and calculation assumptions
All figures are illustrative assumptions, not actual product returns or market quotes. Worked examples were calculated independently by Doug editorial.