A years-old trade built on cheap Japanese money is wobbling again, and it threatens to tank US retirement accounts and the dollar's global standing.

• Investors borrowed free Japanese money for years and poured it into US stocks, bonds, and crypto, inflating those prices with heavy borrowed leverage.
• In 2024, Japan unexpectedly raised rates while the US looked ready to cut, which made the trade unprofitable overnight and caused a violent global sell-off.
• Most 401(k) money sits in the same US stocks this trade helped pump up, so any similar unwind could hit retirement savings hard.
• The trade is rebuilding and may be bigger than before, and now Japan is being forced to dump US government bonds to defend its own currency, pushing US borrowing costs higher.
• Central banks worldwide are already losing faith in the dollar and buying more gold instead, a sign of growing worry about dollar stability.

Outlook: Another rapid unwind of this trade could send US stocks and bonds sharply lower within days and further erode the dollar's status as the world's reserve currency.