“The savings rate was higher, so why is my maturity interest lower than a time deposit?” You can never answer that question without understanding how installment savings actually work. The whole thing comes down to one factor: how long each won you deposit actually sits in the bank. This guide walks through that trap and the savings ladder strategy, current as of 2026.
Korean banking terms, quickly: A time deposit (정기예금, jeonggi-yegeum) is a lump sum you park for a fixed term. An installment savings account (정기적금, jeonggi-jeokgeum) is one where you deposit a fixed amount every month for a fixed term. The "savings ladder" (풍차돌리기, pungcha-dolligi, literally "turning the windmill") is a rotation strategy of opening a new savings account every month — explained in detail below.
Check your maturity interest in the Installment Savings Calculator →
One-line summary
- Even when an installment savings account has a higher headline rate than a time deposit, the actual interest is only about half (54%) of what the headline rate implies
- The reason: each monthly deposit sits in the bank for a different length of time, so the average holding period is roughly half the full term
- The savings ladder is a rotation strategy where you open a new savings account every month, so that a maturity comes due every month starting one year later
Higher savings rate, lower interest — the holding-period trap
At the bank counter, "3.5% per year" looks like the same number whether it's a time deposit or an installment savings account. But the results are completely different.
With a time deposit, you hand over a lump sum once and the entire amount sits in the bank for the full year until maturity. With installment savings, only your first month's deposit gets the full 12 months — your last month's deposit sits for just one month. Even at the same 3.5%, installment savings earns less because the money spends less time in the bank. This isn't a loss; it's just the natural result of how simple interest is calculated.
That's why installment savings interest is calculated separately for each monthly installment and then summed. The formula is simple:
Interest per installment = monthly deposit × annual rate × (months remaining until maturity ÷ 12)
Take a 12-month installment savings account at 3.5% per year with a ₩500,000 monthly deposit as an example:
| Installment | Holding period | Interest (pre-tax) |
|---|---|---|
| 1st | 12 months | about ₩17,500 |
| 6th | 7 months | about ₩10,208 |
| 12th | 1 month | about ₩1,458 |
| Total | average about 6.5 months | about ₩113,000 |
There's a well-known approximation that comes out of this. The effective interest rate of a 12-month installment savings account = annual rate × 13 ÷ 24 ≈ annual rate × 0.542. In other words, the real felt return on a headline 3.5% savings account is closer to about 1.9%.
Deposit vs. installment savings — same rate, same principal
Let's settle the most confusing part head-on. We'll set the total principal to ₩6,000,000 for both, and assume both run at 3.5% per year for 12 months.
| Category | Time deposit | Installment savings |
|---|---|---|
| Deposit method | ₩6,000,000 lump sum | ₩500,000 × 12 months |
| Total principal | ₩6,000,000 | ₩6,000,000 |
| Maturity interest (pre-tax) | about ₩210,000 | about ₩113,000 |
| Savings/deposit ratio | 100% | about 54% |
Same money, same rate — yet the savings account pays only about half the interest of the deposit. That's why the conclusion is: if you already have a lump sum, use a time deposit; if you're still building it up month by month, use installment savings. Installment savings is fundamentally about "building a saving habit," not "maximizing interest."
After-tax interest: subtract the 15.4% interest income tax
Getting the interest isn't the end of it. Interest from time deposits, installment savings, and similar products all counts as interest income, so 15.4% (14% income tax + 1.4% local income tax) is automatically withheld at the time it's paid. Applied to the example above:
| Category | Pre-tax interest | Tax (15.4%) | After-tax interest |
|---|---|---|---|
| ₩6M time deposit | about ₩210,000 | about ₩32,340 | about ₩177,660 |
| ₩500K/month savings | about ₩113,000 | about ₩17,402 | about ₩95,598 |
Once tax is taken out, the felt return shrinks even further. If your annual financial income exceeds ₩20,000,000 you become subject to comprehensive (aggregated) income taxation — geumyung-sodeuk-jonghap-gwase, where interest and dividend income above the threshold is rolled into your overall progressive income tax — so for a large lump sum, an ISA account is also worth considering. An ISA (Individual Savings Account, a Korea-specific tax-advantaged wrapper) is tax-free up to ₩2,000,000 (general type) or ₩4,000,000 (low-income type), and the excess is taxed separately at 9.9% instead of 15.4%.
How the savings ladder works: open every month, rotate maturities a year later
The savings ladder means opening a new installment savings account each month, one at a time. Savings account #1 in January, #2 in February, …, #12 in December. Once you have those 12 accounts running, a maturity comes due every month starting one year later.
| Timing | Action |
|---|---|
| Months 1–12 | Open one new 12-month savings account each month (12 total) |
| Month 13 (next January) | First account matures → recover principal + interest |
| Every month after | Reopen a savings account with the matured cash + new spare funds → rotation |
You can roll the matured cash back into a new savings account, or move it into a higher-rate time deposit. Because there's a maturity every month, when you suddenly need cash you only have to break the nearest maturing account — which prevents the disaster of canceling everything early and losing all the interest.
Pros, cons, and who it's for
Pros
- A maturity comes due every month, so liquidity is good (a lump sum is recovered each month)
- In a rising-rate environment, it's easy to roll matured cash into a higher-yielding product
- Running multiple savings accounts strongly cements a saving habit
Cons
- You have to manage 12 accounts, which is a hassle (tracking maturity dates and auto-transfers)
- The structural limitation remains: savings accounts earn less interest than deposits
- In a falling-rate environment, rotating maturities can actually work against you
In the end, the savings ladder is a structure for liquidity and habit, not for maximizing interest. If you already have a lump sum and can lock it up for a year, a single plain time deposit is more advantageous. It fits early-career workers best — people who want to build a forced saving habit out of their paycheck.
For reference, as of early 2026, 1-year installment savings rates run around 2.5–3.0% per year at major commercial banks, 3.0–3.5% at internet-only banks, and 3.0–4.0% at savings banks (jeochuk-eunhaeng, smaller deposit-taking institutions). Special promotional rates can be higher, so it's best to compare on the Korea Federation of Banks consumer portal before signing up.
Simulate reinvesting your matured cash in the Compound Calculator → — see in a chart how much the lump sums you recover from the ladder grow to after a few years of reinvesting.
FAQ
Q. If a savings account pays 4%, isn't that automatically better than a time deposit at 4%? A. No. The effective rate on a 4% savings account is about 4% × 0.542 ≈ 2.2%. For the same principal, a 4% time deposit pays nearly twice as much interest. Installment savings is a product for "people saving up month by month," not a product to use for a lump sum.
Q. Is the "half the effective rate" formula accurate? A. For a 12-month savings account it's precisely annual rate × 13/24 ≈ 0.542. The first installment is held for 12 months and the last for only 1 month, so the average holding period is about half the term. The longer the maturity, the higher this ratio creeps up.
Q. Is savings interest also taxed? A. Yes. Interest from time deposits, installment savings, mutual installments, and credit-union deposits all counts as interest income, and 15.4% (14% income tax + 1.4% local income tax) is automatically withheld when it's paid at maturity. If your annual financial income exceeds ₩20,000,000, you become subject to comprehensive income taxation.
Q. Are savings accounts covered by depositor protection? A. Yes. Time deposits and installment savings are both protected up to ₩100,000,000 per person per financial institution, combining principal and interest. The cap was raised from ₩50,000,000 to ₩100,000,000 effective September 1, 2025. It applies automatically with no separate application.
Q. Isn't managing 12 ladder accounts way too complicated? A. Setting up auto-transfers and maturity alerts reduces the burden, but it's still genuinely a hassle. If the management feels overwhelming, a realistic alternative is to simplify the ladder to 2–3 savings accounts on a 6-month cycle, or to convert into a single time deposit as the lump sum accumulates.
Related tools
- Simple Interest Calculator — instantly compute maturity interest and after-tax amounts for time deposits and installment savings
- Compound Calculator — simulate long-term returns when reinvesting your matured cash
This article is for informational purposes only. Actual rates, interest, and taxes may vary depending on the product and your individual circumstances. Investment and tax decisions are your own responsibility.