The Tax-Saving Mechanics of the ISA Account

ISA is short for 'Individual Savings Account.' The name sounds grand, but simply put, think of it as an 'all-purpose investment basket with tax benefits attached.'

In this one basket you can hold various products together — deposits, funds, ETFs, and domestic stocks.

What matters is that the country reduces the tax on the profits you earn inside this basket. That's why it's also nicknamed the 'national wealth-building account.'

You can open only one account per person, and it splits into three types by how it's managed: 'brokerage type,' where you buy and sell yourself; 'trust type,' where you entrust trading to the financial firm; and 'discretionary type,' where you hand it over entirely to a professional. The one investors use most these days is the brokerage type, which has low fees and is self-managed.

The way an ISA reduces taxes rests broadly on three devices.

First, loss-offsetting. In an ordinary account, even if you earn 1,000,000 won on product A and lose 1,000,000 won on product B, tax is levied only on the 1,000,000 won earned. The loss is ignored. In an ISA, by contrast, the account's gains and losses are all summed (offset), and tax is levied only on the 'net profit.' In the example above, the net profit is 0 won, so the tax is 0 won.

Second, tax deferral. An ordinary account withholds tax each time interest or a dividend comes in. But an ISA defers the tax calculation until you close the account or it matures. In the meantime, even the money that would have gone out as tax keeps compounding inside the account, so the longer the horizon, the greater the compounding effect.

Third, tax exemption and low separate taxation. Up to a certain amount of net profit is entirely tax-free, and the portion above that is taxed at a rate far lower than the ordinary rate.

Here are the standards in effect as of July 2026.

Tax-free allowance: The general type is tax-free on net profit up to 2,000,000 won; the low-income/farming-fishing type up to 4,000,000 won. (The low-income type has conditions such as prior-year total salary of 50,000,000 won or less.)

Rate on the excess: Net profit above the tax-free allowance is taxed at only 9.9%. This is the base 9% plus 0.9% local income tax. Compared with the 15.4% rate on interest and dividends in an ordinary account, it's clearly lower.

Contribution limit: You can put in up to 20,000,000 won per year, up to 100,000,000 won in total. Any allowance you don't use up this year carries over to the next.

Mandatory holding period: You must maintain it for at least 3 years for the tax benefits to remain fully intact.

The ISA is certainly a good tax-saving tool, but it's not a 'free lunch.' There are pitfalls to know.

The biggest is the mandatory holding period. If you close the account before completing 3 years, the tax benefits you'd received disappear, and you're taxed again at the ordinary rate (15.4%). This means that if it's money you'll need in a hurry, it's hard to tie it up in an ISA for long.

Also, an ISA is merely a 'vessel' that reduces taxes; if the products inside it produce losses, those losses are yours all the same. A tax-saving account absolutely does not protect your principal.

If you invest in overseas stocks or ETFs, the exchange rate affects your return, and you mustn't overlook that management fees apply to each product. If you saved on tax but paid more than that in fees, the point is diminished.

In the end, the ISA has good chemistry with 'funds you'll invest steadily over a long time.' That fits well with the long-term, recurring investing perspective our site keeps emphasizing.