Dollar Up, Won Down: What a Falling S&P Looks Like From Seoul
The won closed at 1,353.3 to the dollar today, against 1,345.3 the day before. That is a 0.59% move in a single session, and it landed on a day when the S&P 500 fell 0.45%. Two small moves on the same day, and for me they pull in opposite directions.
Seen from the US, the session reads as mild anxiety and nothing more. The VIX closed at 17.71, up 2.97%. The ten-year Treasury yield ended at 5.01%, higher by one basis point. The Nasdaq 100 finished essentially unchanged at +0.02%, so whatever was being sold, it was not the large tech names. This is the kind of day that gets one line in a market wrap and is forgotten by Friday.
From Seoul the same session has a second layer. My US holdings are priced in dollars, but I live, spend, and eventually pay tax in won. When I open the brokerage app, the balance has already been converted for me. So a day is never just the index — it is the index multiplied by an exchange rate, and today those two moved against each other.
The Dollar Side of the Same Day
The US Dollar Index closed at 100.34, up 0.69%. The won’s 0.59% weakening is not a separate event from that; it is mostly the same event viewed from the other side. When global money rotates toward dollars, the won is one of the currencies it rotates out of. Nobody in Korea decided anything today.
| close | day | |
|---|---|---|
| S&P 500 | 7,551.8101 | −0.45% |
| Nasdaq 100 | 28,945.0605 | +0.02% |
| VIX | 17.71 | +2.97% |
| US 10-year | 5.01% | +1.0bp |
| US Dollar Index | 100.34 | +0.69% |
| KRW/USD | 1,353.3 | +0.59% |
The last row is the one that needs a warning label for English readers: it counts how many won it takes to buy one dollar, so a rising figure means a weaker won, which means my dollar assets are worth more won than they were yesterday. So the cushioning is real. But I try hard not to call it protection. Nothing about it is contracted, nothing about it is owed to me, and it did not exist as a plan when I bought.
The same risk-off impulse can arrive with a stronger won instead — exporters repatriating, a surplus month, positioning unwinding — and then there is no lift at all. The combination that actually costs me is the reverse of today: US equities down and the won firmer in the same session. I think of that one as the double loss, and it is the reason I refuse to read a day like today as evidence of anything structural.
The yield side is not a reliable guide either. Higher US yields and a stronger dollar tend to travel together, and today both nudged up by small amounts. But the relationship breaks often enough that I have stopped trying to read the won off Treasury yields alone.
Why the Dollar Was Bid
The proximate story was energy and rates. Transport companies are sounding the alarm on fuel prices, and households are being squeezed from the oil side and the rate side at once while the Iran conflict continues. Korea imports nearly all of its crude, and it imports it in dollars. A higher oil price and a weaker won compound each other before the fuel ever reaches a Korean pump — a second multiplication that the American version of this story does not have.
There is also the gap in rates, though it is not a clean comparison. Korea’s base rate stands at 3.00%; the US ten-year closed at 5.01%. One is a policy rate and the other is a bond yield, so setting them next to each other says less than the distance between them suggests, and I will not pretend to know what capital does in response. Exchange rate and base rate figures here come from the Bank of Korea’s Economic Statistics System (ECOS).
It Follows Me to the Tax Return
The FX move does not stop at the account balance. When I eventually sell a US stock, the gain I report in Korea is computed in won, converted at the exchange rate applied on each settlement date — not in the dollars the trade actually happened in. A weaker won at the moment of sale makes the won-denominated gain larger, and the 22% rate applies to that larger number, after the 2.5 million won basic deduction. So today’s cushion is not free. Some of it is a future tax base, quietly growing. As of 2026, that is still how Korean capital gains tax has worked on my overseas shares.
What stays with me is that neither half of today had anything to do with my portfolio. The index fell because of oil and yields on the other side of the world, and the won weakened because money moved toward the dollar for the same reason. I did nothing at all, and the two effects met somewhere in the middle of my account. Most days in this arrangement are like that — the number I end up with is a byproduct of two markets that are not talking to each other about me.
Figures are as of 2026. Korean tax rules change, sometimes yearly. This is my own experience as an individual investor, not tax advice.