Deposit and Installment Savings Interest Calculator (After-Tax Payout)
Enter a lump-sum deposit (예금) or monthly installment savings (적금) to get simple interest and the maturity amount after the 15.4% tax is deducted.
Show how it is calculated
Deposit: Pre-tax interest is principal × annual rate × months ÷ 12. If you deposit 10,000,000 won at 3.5% for 12 months, it is 10,000,000 × 0.035 × 12 ÷ 12 = 350,000 won.
Installment savings: Money paid in the first month earns interest for 12 months, the second month's for 11 months, and the last month's for only 1 month. So the formula is monthly payment × (months × (months + 1) ÷ 2) × annual rate ÷ 12. For 500,000 won a month at 4% for 12 months: 500,000 × 78 × 0.04 ÷ 12 = 130,000 won.
Tax: 14% of the pre-tax interest is deducted as income tax, and 10% of that income tax is deducted as local income tax. Each tax is rounded down to the nearest 10 won. For the deposit above, income tax of 49,000 won and local income tax of 4,900 won are deducted, leaving 296,100 won in interest.
How to use
First choose deposit or installment savings. For a deposit the amount field means 'amount to deposit'; for installment savings it means 'monthly payment'. You can type the amount with commas, like 1,000,000. For the interest rate, enter the annual pre-tax rate shown by the bank, as a number without the % sign.
Enter the term in months: 12 for a one-year product, 6 for six months, 24 for two years. The result shows the amount you receive at maturity, split into pre-tax interest, income tax and local income tax.
How different are simple and compound interest?
With simple interest (단리), interest is paid only on the original principal. With compound interest (복리), interest is also paid on the interest already added. This calculator uses simple interest, which is common for fixed-term deposits and installment savings at Korean banks.
In numbers: 10,000,000 won at 3.5% for one year gives 350,000 won of pre-tax interest under simple interest. With monthly compounding, where interest is added to the principal each month, it is about 355,669 won, a little over 5,600 won more. The gap is small for 1 to 2 years, but it grows with longer terms and higher rates. If a product's description says 'monthly compounding', expect slightly more interest than this calculator shows.
Why installment savings interest is less than 'principal × 4%'
If you pay in 500,000 won a month for a year, your principal is 6,000,000 won. Multiplying by 4% gives 240,000 won, and it is easy to expect that much at maturity. But the actual pre-tax interest is 130,000 won, a little over half.
The reason is that each payment stays at the bank for a different length of time. The 500,000 won paid in January earns interest for 12 months, but the 500,000 won paid in December earns it for only 1 month. On average, the whole 6,000,000 won is held for only about 6.5 months. Compare that with putting the same 6,000,000 won in a one-year deposit, which earns 240,000 won pre-tax. So even if an installment savings rate looks higher than a deposit rate, the interest you actually receive can be smaller.
The 15.4% tax and products that reduce it
According to the National Tax Service (국세청) withholding tax table, the income tax rate on ordinary interest income for individuals is 14%. Local income tax (10% of the income tax) is added, so, as the National Tax Service tax help center explains, '14% (15.4% including individual local income tax)' is withheld. The bank deducts it when it pays the interest, so you usually do not need to file separately.
However, if your combined interest and dividend income (financial income) exceeds 20 million won in a year, you may have to report it together with your other income as comprehensive income tax. The National Tax Service states that if annual financial income is 20 million won or less, withholding by the financial institution settles the tax obligation.
Some products reduce tax. Under Article 88-2 of the Restriction of Special Taxation Act (조세특례제한법), the tax-free comprehensive savings account (비과세종합저축), based on the text checked on 2026-10-13, charges no income tax on interest for up to 50 million won of principal per person, if you join by December 31, 2028. Eligible people include residents aged 65 or older who receive the basic pension, persons with disabilities, independence merit holders and their surviving families, and basic livelihood recipients. Article 89-3 of the same Act covers reduced tax on deposits at cooperatives such as Nonghyup, Suhyup and Shinhyup (조합등예탁금); the eligibility, limits and deadlines have changed several times, so be sure to check the current terms with the institution you plan to join. This calculator does not distinguish these products and calculates everything at the standard 15.4%.
Basis of the calculation
Base year: 2026
- National Tax Service withholding tax rate table (interest income, individual, other interest income 14%) — checked 2026-10-13
- National Tax Service tax help center, financial income consultation case (15.4% withholding, 20 million won financial income threshold) — checked 2026-10-13
- Korea Law Information Center, Restriction of Special Taxation Act (조세특례제한법) Article 88-2 (tax-free comprehensive savings) and Article 89-3 (deposits at cooperatives) — checked 2026-10-13
Tax rates and tax-exemption schemes can change when tax law changes, so we recheck and update them every year.
Common mistakes and things to watch for
- Entering the bonus rate as if you will always get it: The highest advertised rate often requires conditions such as salary transfers or card spending. It is better to calculate twice, once with the base rate you are sure to get and once with the highest rate, and look at the range.
- Cancelling early: If you cancel before maturity, an early-termination rate lower than the contract rate usually applies. This calculator assumes you keep the product until maturity.
- Skipping installment payments: If payments fall behind, the maturity date may be pushed back or the interest may be reduced. The result assumes you pay the same amount on the same day every month without missing any.
- Mixing after-tax and pre-tax rates: Bank rates are usually quoted before tax. If you enter an after-tax rate here, tax will be deducted twice.
Frequently asked questions
If I put 10,000,000 won in a one-year deposit at 3.5%, how much do I actually receive?
Pre-tax interest is 350,000 won. After deducting 49,000 won of income tax and 4,900 won of local income tax, 296,100 won of interest remains. With the principal, you receive 10,296,100 won at maturity.
Installment savings rates are higher than deposit rates, so why is the interest smaller?
Because you pay in monthly, the average time your money stays at the bank is shorter. For a 12-month installment savings, the whole principal is effectively held for only about 6.5 months on average, so it earns less interest than a deposit at the same rate.
Where does 15.4% come from?
It is the 14% income tax on interest income plus 1.4% local income tax, which is 10% of the income tax.
Can it calculate compound-interest products?
This calculator only does simple interest. A monthly-compounding product pays slightly more than the result. For 10,000,000 won at 3.5% for one year, the pre-tax difference is a little over 5,600 won.
For a tax-free product, can I just ignore the tax in the result?
For a product with no income tax, such as the tax-free comprehensive savings account, the 'pre-tax interest' in the result is close to the interest you receive. However, some products have other taxes or limits, so check the guidance from the institution you join.
This is a reference calculation; official guidance from the relevant institution takes precedence.
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