Why the Dollar-Won Rate Moves With Interest Rates

Headlines like "the US hikes one more time" or "the Fed holds steady" land, and the dollar-won rate jolts that day. Why does one line of US rate news shake the very exchange rate that touches your account? Once the mechanism clicks, the next FX article reads a lot easier.

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The simplest reason exchange rates move

In the end, exchange rates come down to how many people want to buy dollars versus how many want to sell. More buyers, dollar gets pricier — which, for someone holding won, means the rate goes up. As in, you need 1,400 won to buy a single dollar.

Who's buying and selling? Foreign investors, Korean companies, Korean individuals, the Bank of Korea, big players holding US assets — they all participate. The biggest flow comes from capital movement. When large money moves from Korea to the US, won has to be sold and dollars bought, which pushes the rate up. The reverse — money flowing into Korea — sells dollars and buys won, pulling the rate down.

The biggest factor steering those capital flows is the gap between the two countries' interest rates. That's why US rate news shakes the exchange rate.

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Why money flows toward higher rates

Think about it personally. Imagine a one-year deposit at a Korean bank pays 3% while the same at a US bank pays 5%. Setting aside currency moves, where would you put your money? Obviously the US. That extra two percentage points just flows in.

Big money worldwide runs the same math. If US Treasuries pay 5% and Korean government bonds pay 3%, capital naturally tilts toward US Treasuries. To get there, you sell won and buy dollars. Dollar demand rises, the rate climbs.

As of 2026, the US policy rate sits in the 3.75 to 4.0% range while Korea's is around 2.5%. The spread is roughly 1.5 percentage points. Whether that spread tightens or widens drives the FX trend each time. A signal that the US will hike again means the spread widens, capital tilts further to the dollar, and the rate moves up.

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Why you can't just watch the current spread

One more layer. Looking only at the current spread doesn't explain everything. Markets always look at the future spread.

The Fed releases the dot plot at policy meetings. Each dot shows where one official thinks rates should go from here. Markets read that dot plot to estimate where the spread is heading. The current spread might be 1.5 percentage points, but if the US signals two more cuts next year, that narrows the spread — and the dollar's appeal slips.

That's why the rate often jolts even on a meeting that just held rates steady. The number itself matters less than the forward signal.

This is what's called the forward exchange rate concept. Today's rate is really a price that already prices in future spread expectations.

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Two other things FX watches besides rates

Rates are the biggest factor, but two more move the exchange rate: trade flows and risk-off sentiment.

Trade flows are the gap between exports and imports. When Korea exports to the US and earns dollars, those dollars get converted back into won — so dollar selling rises. When Korea imports a lot from the US, dollars have to be bought to pay for it — dollar buying rises. Strong export periods put downward pressure on the rate; heavy import periods push it up.

Risk-off sentiment hits harder. When a global crisis breaks out, people run to safer assets. The US dollar is the biggest of those safe havens. So during crises, the dollar strengthens and other currencies weaken. The Korean won, classified as an emerging-market currency, tends to weaken right along with them during a panic.

That's why the rate sometimes refuses to drop even when the US cuts. Risk-off sentiment can overwhelm the rate effect.

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What does a rising rate do to your account?

A rising exchange rate hits two groups directly.

First, people invested in US assets. If you bought an S&P 500 ETF with won, a rising exchange rate actually helps you. The same dollar value converts to more won. Even if the US stock didn't move, a 10% rise in the rate adds about 10% to your won-denominated balance.

Second, people buying things from the US or traveling abroad. The same $100 item costs 130,000 won when the rate is 1,300, but 140,000 won when the rate is 1,400. Your wallet directly gets lighter.

Even if you just sit on your won-paid salary, a rising rate quietly shrinks your global purchasing power. The number in your account stays the same, but measured in US goods, you've gotten poorer.

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So where does the rate end up?

That's the hardest question. Almost no one calls it precisely. But the big picture comes back to the US-Korea spread direction.

When the US enters a cutting cycle, the spread tightens and a weaker-dollar pressure builds. When the US hikes or holds steady for a long stretch, the spread stays wide and the dollar pressure persists. Whether the Bank of Korea cuts before or after the Fed also shifts the spread.

Add trade surpluses or deficits, global crisis risk, and foreign capital flows on top. The rate rarely runs in one direction for long — most of the time, it churns in a range.

You don't have to call the rate exactly. As long as you watch "which way the spread is moving" when US rate news drops, the daily moves start to make sense. That alone gets you much further in reading the FX market.