When Treasury Yields Hit 5%, but the Won Gets Stronger
The US 10-year Treasury yield closed at 5.00% on September 15, up 3.5 basis points from 4.96% the session before. In pure return terms it was an ordinary day, and the headline number is itself a rounding — the move only just carries the yield over the line. But 5.00% is a round number, and round numbers do something to people that 3.5 basis points on their own do not. I read all of it after the close, which is the usual condition of trading US markets from Seoul.
For a saver in Korea the number lands differently than it does in New York. A US government bond yielding 5.00% against a domestic policy rate of 3.00% is not a subtle proposition. It is the kind of gap that makes people move money, and it is the reason dollar bond exposure keeps coming up in conversations here that used to be about stocks only.
The catch showed up in the other column. The KRW/USD reference rate closed at 1,345.3, down 0.08% on the day — a stronger won. Small, almost nothing. What makes it worth a second look is that the dollar itself was not weak: the US Dollar Index closed at 99.612, up 0.15%. The dollar gained ground broadly and lost a little against the won anyway.
That combination is the thing a Korea-based investor has to hold in mind and a US-based one never does. A Treasury pays its coupon in dollars. I earn in won, I will spend in won, and the yield only becomes real to me after it has been converted back. There are two legs to the position and they are priced in two different markets. On September 15 the first leg got better and the second leg got slightly worse.
Two markets, one position
| What | Close | Change on the day |
|---|---|---|
| US 10-year Treasury yield | 5.00% | +3.5bp |
| KRW/USD reference rate | 1,345.3 | -0.08% |
| US Dollar Index | 99.612 | +0.15% |
| S&P 500 | 7,585.73 | -0.45% |
None of this happened in a vacuum. The market is positioning for a Fed rate hike, and the fight over counting the votes inside the committee is a story of its own right now. Equities took it the way you would expect. The S&P 500 closed at 7,585.73, down 0.45%, the Nasdaq 100 down 0.65% and the VIX at 17.2, up 0.58%. Nobody panicked. A higher risk-free yield simply makes everything else a little less attractive, and the market marked it down accordingly.
The timing question I cannot solve
The temptation is obvious: wait for the yield to go a little higher and the won to go a little stronger, then convert and buy at the best of both. I have never once managed this. The two variables do not cooperate, and the rare days when both look good together are usually days when something has gone badly wrong somewhere else. In my case I gave up on optimizing the pair and settled for two rules instead — convert on a schedule rather than on a view, and leave dollar income in dollars unless I actually need the won.
The second rule is not a solution, only a deferral. Interest earned in dollars is still money that has to come home someday, at a rate I do not know yet. What it buys is the ability to choose the year, which matters because every conversion has a cost attached — part of what it actually costs to buy VOO from Korea, and part of what it costs to sell it too.
There is also a tax seam here that does not exist for a US investor. Gains from selling a US stock fall under the overseas capital gains regime, taxed at 22% with the 2.5 million won annual deduction. Interest does not travel through that door at all — it is financial income, a separate regime with its own rate and its own filing, and those figures are not ones I am going to quote from memory. Same broker, same account, two different sets of paperwork. That is worth knowing before a yield story convinces anyone to shift the mix.
The version where both legs move against you at once — a falling US asset and a won that keeps getting stronger — is the double loss. September 15 was only half of that, on the currency side, and by a rounding error at that. It is still the half that gets ignored.
What strikes me is the asymmetry in how the two numbers get reported. The 5.00% print will be everywhere — headlines, Korean coverage of US markets, brokerage push notifications at seven in the morning. The 0.08% move in the won will be in none of them. Over a long holding period that second number also lands on what I actually end up with, and it moves every single day whether or not anybody writes it up.
Won reference rate and Korean policy rate from the Bank of Korea’s Economic Statistics System (ECOS); the US yield, index and dollar figures are session closes. All figures are as of the September 15, 2026 close. Korean tax rules change, sometimes yearly. This is my own experience as an individual investor, not tax advice.