What Is the Yen Carry Trade? How an Interest-Rate Bet Unwinds All at Once

Why a 12% Nikkei Crash Traced Back to a 0.15-Point Rate Hike

On August 5, 2024, Japan's Nikkei 225 fell roughly 12% in a single day — its worst one-day drop since Black Monday in 1987. Korea's KOSPI fell about 8% the same day, the S&P 500 dropped around 3%, the Nasdaq fell about 6%, and the VIX, the market's "fear gauge," spiked roughly 70% in a day to its highest level since the early COVID crash. What triggered all of this wasn't a recession warning or an earnings shock. It traced back to the Bank of Japan raising its policy rate from 0.1% to 0.25% — a move of just 0.15 percentage points. That a rate change this small could shake global equity markets simultaneously seems disproportionate on its face. At the center of the chain reaction was the yen carry trade, a trading structure quietly woven through funding markets worldwide. This lesson covers what a carry trade actually captures, why unwinding one can drag equity markets down with it, and what the mechanism looked like in a real, recent case.

The Basic Structure: Turning a Rate Gap Into Profit

The idea behind a carry trade is simple. Borrow in a currency with a near-zero interest rate, convert the proceeds into a currency with a much higher rate, and pocket the difference (the "carry"). Say you borrow yen at close to 0% interest, convert it into dollars or won, and invest in bonds, deposits, or equities yielding around 4% a year. If the funding cost is near zero and the return is 4%, then — assuming the exchange rate doesn't move — you're left with close to a 4-percentage-point annual spread, essentially for free. Because Japan has held ultra-low or zero interest rates for decades since its early-1990s bubble collapse, the yen has become the textbook "funding currency" for this kind of trade worldwide. The Swiss franc has played a similar role at times, for the same reason: the Swiss National Bank kept rates near or below zero for years. The borrowed money flows into a wide range of assets — US Treasurys, US megacap tech stocks, emerging-market bonds, corporate credit, even crypto — which is why the yen is sometimes described less as "Japan's currency" and more as a hidden funding source for risk-taking across global markets.

Why the "Free" Profit Isn't Actually Free: Currency Risk

The critical point to understand is that the real danger in a carry trade isn't the interest cost of the borrowed money — it's the exchange rate. For the trade to work, the funding currency can't appreciate too much before the position is closed. Eventually the investor has to convert the foreign-currency returns back into yen to repay the loan, and if the yen has strengthened in the meantime, each unit of foreign currency now buys fewer yen — making the debt harder to repay. A sharp enough move can wipe out the entire interest-rate spread and then some. In theory, a concept called interest rate parity predicts that a lower-yielding currency should appreciate over time by roughly the amount needed to offset the rate gap, closing the opportunity. In practice, this relationship holds poorly, and low-yield currencies have often stayed weak for extended stretches, letting carry trades earn steady profits for years at a time. The catch is that those steady gains can be erased in a matter of days by one abrupt reversal. This asymmetric risk profile — small, steady gains against the possibility of a sudden, outsized loss — is sometimes described with the image of "picking up pennies in front of a steamroller."

How Leverage and Crowding Amplify the Risk

The risk compounds further because most carry trades aren't run unlevered. Hedge funds, institutional investors, and retail traders alike commonly use forwards, swaps, or margin to scale up position size well beyond their own capital. With leverage in place, even a 1–2% move in the exchange rate translates into a much larger swing in profit or loss. On top of that, the carry trade is a classic crowded trade — large numbers of participants worldwide putting on structurally identical positions (short yen, long higher-yielding assets) around the same time. The longer low rates and low volatility persist, the more this looks "safe enough" to more participants, and the larger the aggregate position built up across the system becomes. The real danger shows up when that crowd tries to exit at once. In a bulletin analyzing the August 2024 episode, the Bank for International Settlements (BIS) described the shock as amplified by "procyclical deleveraging and margin increases." Broken into steps: ① the yen starts appreciating; ② leveraged carry positions start showing losses; ③ traders facing margin calls sell the risk assets they bought with borrowed yen and buy yen back to repay their loans; ④ that combination of asset selling and yen buying pushes asset prices down and the yen up further; ⑤ which triggers margin calls elsewhere, restarting the loop. Because so many participants are trying to exit through the same door at once, the unwind doesn't happen gradually — it compresses into days, or in the extreme case, a single trading session.

The August 2024 Unwind, by the Numbers

The real-world sequence makes the mechanism concrete. On July 31, 2024, the Bank of Japan raised its policy rate from 0.1% to 0.25% and signaled it was open to further hikes and balance-sheet reduction. Two days later, on August 2, a weak US jobs report (114,000 new jobs versus roughly 175,000 expected) fueled expectations that the Federal Reserve would cut rates faster than markets had priced in. With both events landing close together, expectations for a further-narrowing US–Japan rate gap spread quickly, and the yen appreciated sharply over just a few days. That appreciation triggered losses on leveraged carry positions and set off the feedback loop described above — producing the Nikkei's roughly 12% single-day drop, the KOSPI's roughly 8% drop, declines of about 3% and 6% in the S&P 500 and Nasdaq, and a roughly 70% one-day spike in the VIX. The BIS estimated the scale of yen-funded carry positions unwound in the episode at somewhere around ¥40 trillion (roughly $250 billion), while noting that data limitations likely make this an undercount. What's notable is that despite the size of the shock, markets didn't experience outright dysfunction — and within a matter of weeks, low-volatility, yen-funded carry positions were already being rebuilt. The structure itself hadn't disappeared; prices had simply reset.

Is the Unwind Risk Over? The Bank of Japan Keeps Hiking

The Bank of Japan didn't stop normalizing policy after August 2024. It raised its rate to 0.5% in January 2025, hiked again in December 2025 to reach its highest level in roughly 30 years, and hiked once more in September 2026 to 1.25% — its highest level since 1995. Notably, the September 2026 move came just three months after the previous hike, a pace widely read as a marked acceleration in tightening. And yet the carry trade hasn't gone away. As of late 2026, reporting suggests yen-funded carry positions worth an estimated several hundred billion dollars (estimates vary meaningfully by source) remain spread across everything from US Treasurys to corporate credit. At the same time, as the rate gap itself continues to narrow, commentary increasingly frames the trade as "no longer a free lunch" compared with its heyday. This illustrates something important: the carry trade isn't a one-off event that resolves after a single shock — it's a structural flow that keeps rebuilding itself as long as an interest-rate gap exists between the funding currency and the target currency. That's also why every fresh BOJ rate hike tends to revive the same market question: could this trigger another round of unwinding?

What This Means for Investors

Even investors who never run a carry trade themselves have reason to understand the mechanism, because it isn't confined to the FX market — it's wired directly into global equity markets. Since borrowed yen also funds purchases of US megacap tech stocks and emerging-market assets, a sudden, sharp yen rally can drag down assets that look, on the surface, entirely unrelated to Japan. So when a headline reads "the Bank of Japan raised rates" or "the yen surged," it's worth reading it in the same cross-border-flow framework covered in How Interest Rates Affect Stock Valuations and How Currency Moves Affect Corporate Earnings, rather than filing it away as a Japan-only story. A related idea shows up in crypto markets too: funding rate arbitrage captures a spread in a similar way, just funded by perpetual futures funding rates instead of a national currency — the underlying risk, that a steady-looking spread can reverse abruptly, is the same.

Takeaway

• A carry trade borrows in a low-rate currency, most commonly the yen, and invests the proceeds in higher-yielding assets, capturing the rate gap as profit.
• The real risk isn't the borrowing cost — it's the exchange rate. A sharp appreciation of the funding currency can erase the entire rate-gap profit, and more.
• Because carry positions are commonly leveraged and structurally crowded, yen appreciation can set off a feedback loop: losses trigger margin calls, margin calls force selling of risk assets and buying of yen, which pushes the yen up further and repeats.
• In August 2024, a BOJ rate hike landing alongside a weak US jobs report triggered this loop, producing a roughly 12% single-day Nikkei crash and a synchronized global equity selloff — a real-time example of a carry unwind spilling into stock markets.
• The carry trade isn't a one-time event; it keeps rebuilding as long as a rate gap exists, and continued BOJ tightening keeps the risk of another unwind on the market's radar.

FAQ

Do individual investors run yen carry trades too?

Institutions and hedge funds dominate the trade, but an individual borrowing in a low-rate foreign currency to invest in higher-yielding assets is running a structurally similar position. Because leverage and currency risk both scale up together, it's a hard trade to size correctly without fully understanding the mechanics.

Does a yen carry unwind actually affect markets like Korea's?

Yes — the KOSPI fell roughly 8% on August 5, 2024. Even markets with no direct exposure to the carry trade itself tend to get hit hard during a broad risk-asset unwind, and emerging-market-style indexes like the KOSPI have historically been among the more volatile in that kind of episode.

Does every BOJ rate hike trigger a crash like this?

No. The August 2024 episode was severe largely because the rate hike landed at the same time as a separate shock (the weak US jobs report), at a moment when a large volume of carry positions had already built up. The market impact of a given hike depends heavily on how crowded the existing positioning is and whether other bad news hits at the same time.

⚠️ This article is for informational purposes only and is not investment advice. You are solely responsible for your own investment decisions.