Editor’s note: The charts and figures presented in this post have been revised to correct for a minor coding error. The updated results are the same qualitatively and somewhat stronger quantitatively. October 8, 2025.

Trading activity in benchmark U.S. Treasury securities now concentrates on the last trading day of the month. Moreover, this stepped-up activity is associated with lower transaction costs, as shown by a smaller price impact of trades. We conjecture that increased turn-of-month portfolio rebalancing by passive investment funds that manage relative to fixed-income indices helps explain these patterns.






