Installment Savings vs. Time Deposits: What's the Difference, and How to Pick the Right One

Open your banking app and you'll see a flood of similar-looking products: 'time deposit, 3.8% per year,' 'installment savings, 4.2% per year.' Going by the numbers alone, the installment savings rate looks higher, yet it's common for the interest actually paid at maturity to be greater on the time deposit. Why? Because the two products differ in the very 'way you put money in.' Once you understand this difference, you can choose far more shrewdly the product that fits your lump sum and your salary flow. (This article is reference material for informational purposes and is not a solicitation for any specific product.)

One-line definition: a time deposit 'stores a lump sum,' installment savings 'builds one up'

A time deposit is a product where you place a lump sum you already have all at once and leave it until maturity. For example, you might lock away 12 million KRW for one year. An installment savings account, by contrast, is a product where you deposit a fixed amount each month to build up a lump sum. The structure is to deposit 1 million KRW each month, 12 times, to accumulate 12 million KRW. Both pay principal plus interest at maturity, but the 'period' over which interest accrues is completely different.

Why the same 4% per year produces a twofold difference in interest

With a time deposit, the entire lump sum you deposit at the start earns interest for the full year. Place 12 million KRW at 4% per year for one year, and the pre-tax interest is 12 million KRW x 4% = 480,000 KRW. Installment savings, however, are different. The 1 million KRW you deposit in the first month earns 12 months' worth of interest, but the 1 million KRW you deposit in the final, 12th month earns just 1 month's worth of interest. On average, the money is effectively on deposit for only about half the period, so even at the same 4% per year the pre-tax interest comes to only about 260,000 KRW.

The tax bite is the same: 15.4% interest income tax

Whether it's a time deposit or installment savings, the interest you receive is subject to a 15.4% interest income tax (14% income tax + 1.4% local income tax). For the deposit above with 480,000 KRW in pre-tax interest, about 73,920 KRW is withheld as tax, leaving a take-home amount of about 406,080 KRW. Remember that every quoted rate is 'pre-tax,' and that the tax is withheld at source - the bank deducts it for you before paying out.

Is the principal guaranteed? 50 million KRW deposit protection

Both time deposits and installment savings are covered by deposit protection. Even if a bank goes bankrupt, the Korea Deposit Insurance Corporation guarantees principal and interest combined up to a maximum of 50 million KRW per person, per financial institution (reflecting the protection ceiling raised in 2025). The key point is that the limit is 'per bank.' If you deposit more than 50 million KRW at a single bank, the excess may not be protected, so if your lump sum is large, it's safer to split it across several financial institutions.

Choosing by situation

• You already have a lump sum -> a time deposit. Suitable for safely putting to work money that arrived all at once, such as a bonus, severance pay, or a jeonse deposit.
• You need to save up month by month -> installment savings. Good when you want to force a saving habit out of your salary.
• You don't know when you'll need it -> a freely-accessible parking account/CMA. The rate is low, but your money isn't locked up.
• Money you won't touch for over a year and want to shelter from tax -> use an ISA account. It can hold installment savings and deposits too, with tax-free and separate-taxation benefits.
• Preparing for retirement plus aiming for a year-end tax refund -> a pension savings account/IRP. Different in character from savings and deposits, but the tax credit is powerful.

One step further: pairing in a tax-saving account

With plain savings and deposits you have to pay the full 15.4% interest income tax, but place them in an ISA (Individual Savings Account) and net profit up to 2 million KRW (4 million KRW for the working-class type) is tax-free, with any excess taxed separately at 9.9%. For retirement funds, combining a pension savings fund and an IRP and contributing up to 9 million KRW per year earns a tax credit of 13.2-16.5% (16.5% for total salary of 55 million KRW or less). Maxing out the 9 million KRW per year means getting back up to 1,485,000 KRW through year-end tax settlement - closer to a sizable 'fixed return' than to simple deposit interest (note, however, there are penalties for early termination before age 55).

Getting a feel for time with compounding and the Rule of 72

You can quickly gauge how long it takes for your money to double using the 'Rule of 72.' 72 / annual rate (%) = roughly the number of years for the principal to about double. At 4% per year that's 72 / 4 = 18 years; at 6% per year, 72 / 6 = 12 years. Savings and deposits are safe but, with their low rates, take a long time to double. That's why, rather than parking your entire portfolio in savings and deposits alone, the general asset-management principle is to diversify between safe assets (savings/deposits) and risk assets (stocks, ETFs, etc.) in line with your own risk tolerance.

Savings and deposits are less an 'engine for growing money' than a 'base camp for not losing it.' Put your emergency fund and short-term goal money here; put long-term money to work alongside tax savings and diversification.

In short, the basic formula is 'lump sum -> deposit, building up -> installment savings.' Add tax savings with an ISA or pension savings, throw in the Rule of 72 for a sense of timing, and the same money can produce different results. Rates and conditions change by period and by institution, so before signing up be sure to check the latest terms and your own timing for using the funds. This article is intended to provide general financial information; it does not solicit enrollment in any specific product or guarantee returns.