ToolwebHow to use this tool
- Choose a one-off deposit or installments at the start of each month.
- Enter amount, annual rate, months, simple/monthly compound convention and applicable tax rate.
- Compare principal, pretax/after-tax interest and the monthly accumulation schedule.
One year at 3.5% on KRW 10 million
- Input and settings
- Deposit KRW 10,000,000; 3.5% annually; 12 months; simple interest; withholding 15.4%
- Result
- Pretax interest KRW 350,000; after-tax maturity KRW 10,296,100
Assumes monthly periods and withholding at maturity; comprehensive financial-income taxation is excluded.
Installment timing affects interest
Beginning-of-month installments earn different numbers of periods: the first deposit earns the full term and the last earns one month. This differs from multiplying every deposit by the entire term.
Simple interest accrues only on contributed principal; monthly compounding also earns on previously accumulated interest. The schedule separates deposits from interest so that compounding is not mistaken for extra contributions.
Assumptions behind maturity withholding
The illustrative 15.4% withholding combines ordinary 14% interest-income tax and local tax of 10% of that tax. Enter the actual combined rate for an exempt or preferential product.
Interest is rounded to whole KRW at the end, with withholding applied once at maturity. Products using exact day counts, monthly taxation, conditional bonus rates or early-withdrawal rates follow different contractual formulas.
Common questions
Why is total contributions × annual rate too large for installments?
Later installments have not been invested for a full year. The monthly balance table reflects the shorter remaining earning period for each contribution.