The basic mechanics
Suppose Japan has a 0% policy rate and Australia has a 4% policy rate. A carry trader borrows ¥100 million at 0%, converts it to AUD, invests in Australian bonds at 4%, and earns 4% annually as long as the exchange rate doesn't move against them. If AUD/JPY remains stable, they earn 4% per year essentially risk-free. If AUD appreciates against JPY, they earn an additional FX gain. The carry trade's profit = interest rate differential ± exchange rate move.
Why the carry trade "works" (and why it shouldn't)
Standard economic theory (uncovered interest rate parity) predicts that carry trades should earn zero on average — the high-yield currency should depreciate by exactly the interest rate differential, eliminating the profit. In practice, this doesn't happen consistently, at least in the short to medium term. Currencies with high interest rates often appreciate rather than depreciate (the "forward premium puzzle"), making carry trades persistently profitable. The explanation: risk premium. Carry trade returns compensate for the risk of sudden, sharp losses during crises.
Carry crashes: the unwind
When global risk appetite falls sharply — a financial crisis, a geopolitical shock, a sudden repricing event — carry trades unwind simultaneously. Traders rush to close their positions: they sell the high-yield currency and buy the funding currency. This self-reinforcing flow causes the funding currency to surge (often JPY or CHF, historically) while the high-yield currencies collapse. The 2008 crisis saw AUD/JPY fall from 104 to 55 in six months — a 47% move that wiped out years of carry gains in weeks. The yen surge of August 2024 was another dramatic carry unwind.
Carry in other asset classes
The carry concept extends beyond FX. In fixed income, carry means buying higher-yielding bonds and funding with lower-yielding short-term borrowing. In equities, carry means buying high-dividend stocks financed with borrowed capital. In commodities, carry relates to the cost of storing physical goods (backwardation vs. contango in futures curves). The universal pattern: carry strategies collect risk premium steadily until the underlying risk materialises and produces large losses.
"The carry trade is like picking up nickels in front of a steamroller — the expected value may be positive, but the distribution of outcomes has a very fat left tail." — A FX trader's description
What this means for you
Large-scale carry positioning — visible through futures data (CFTC positioning reports) and option skew — creates predictable volatility dynamics. When JPY short positioning is historically extreme, the potential for a violent yen squeeze is elevated. Understanding carry dynamics explains movements in "safe haven" currencies (JPY, CHF, USD) that appear disconnected from the economic fundamentals of those countries — they are driven by unwinding of leveraged carry positions, not domestic economic developments.