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Saving a fixed amount every month is the most basic yet most reliable way to build a lump sum — that is the regular installment savings (Jeonggi-jeokgeum). It is the most representative savings product: you deposit a fixed amount each month for an agreed period and receive your principal plus the promised interest at maturity.
It is ideal for planned saving toward concrete goals such as travel funds, a home down payment, or tuition. The built-in discipline helps you resist spending temptation and form a steady saving habit.
This calculator is your smart guide to reaching those goals. Enter your monthly deposit, interest rate, term, and tax option to see exactly how much you will receive at maturity — and compare products to choose the best one.
Term Glossary
- Installment savings
- A savings product where you deposit a fixed amount monthly and receive principal plus interest at maturity.
- Simple interest
- Interest calculated only on the principal deposited each month; commonly used for installment savings.
- Monthly compounding
- Interest earned each month is added to principal so next month interest is earned on principal + interest; better than simple interest over long terms.
Installment savings interest is calculated mainly as simple interest or monthly compound interest. The method you choose changes your maturity payout, so understanding the difference matters.
1. Simple Interest
The most basic method: interest is applied over the deposit period to the principal deposited each month only.
※ Each month's deposit is held for a different period (first month 12 months, last month 1 month), hence the formula.
2. Monthly Compound Interest
Each month's interest is added to principal, and next month interest is earned on principal + interest — the snowball effect grows over time.
※ Monthly rate = annual rate / 12
3. Tax Calculation
- General taxation: 15.4% of interest income (14% income tax + 1.4% local tax)
- Tax preference: 9.5% of interest income (for qualifying products, within limits)
- Tax-free: 0% (when qualifying for tax-free composite savings, etc.)
Example (100,000/mo, 12 months, 3% annual, simple, general tax)
Total principal = 100,000 × 12 = 1,200,000
Total interest = 100,000 × (12×13/2) × (0.03/12) = 19,500
Tax = 19,500 × 15.4% = 3,003
Net payout = 1,200,000 + (19,500 − 3,003) = 1,216,497
💡 Getting the Most from Installment Savings
1. Simple vs Compound — Myth and Truth
Compound is often said to be always better, but for a 1-year installment plan the difference from simple interest is tiny. Over longer terms and larger deposits, however, compounding becomes powerful.
2. Rate Shopping Pays — The 0.1% Butterfly Effect
The more you shop, the higher your rate. Don't stick to your main bank — compare non-face-to-face products from internet-only and savings banks.
3. Automate: Save First, Spend Later
Set payday = transfer day. Auto-transfer to savings the moment salary arrives, removing the temptation to spend.
4. Don't Miss the Tax-Free Composite Savings Limit
If you are 65+, disabled, or meet other criteria, interest income up to a 50M KRW combined limit across all banks is tax-free.