A fifth of month-end Treasury trading now happens around 4 p.m.
Serguey Asael Shinder2 min readTrading in US Treasury securities is increasingly clustered around the times when fixed-income indexes set their closing prices, according to a Liberty Street Economics post published by the New York Fed on 22 September. The concentration is sharpest on the last trading day of the month, when indexes are rebalanced.
The Treasury market has no exchange-mandated close, so index providers choose when to take their prices. For years 3 p.m. Eastern was the standard. On 14 January 2021, Bloomberg - one of the largest fixed-income index providers - moved the strike time for its US dollar indexes to 4 p.m.; the authors note reports that one reason was to reduce tracking error for funds that must price portfolios at 4 p.m. Trading followed. Using BrokerTec interdealer data on on-the-run notes and bonds, the post shows the share of daily volume in the ten minutes around 3 p.m. rising from 2.3% in 2016 to 3.4% in 2020, then plunging after the change, while the share around 4 p.m. grew from 2.5% in 2021 to 3.5% in 2025.
Month-end days magnify the effect. The share of volume around 3 p.m. on those days rose from 8.1% in 2016 to 12.1% in 2020; around 4 p.m. it rose from 11.6% in 2021 to 20.4% in 2025. In 2025 the half hour from 3:45 to 4:15 p.m. accounted for more than a quarter of total activity on month-end days. An earlier post by the same team found overall Treasury volume on the last trading day of the month to be about 58% higher than on other days, a concentration that has grown over the past decade and has been associated with better liquidity.
What it means
The world's most important bond market has, in effect, acquired a closing auction without anyone designing one. Passive and benchmarked investment has grown large enough that the moment an index takes its price sets when a large share of trading happens.
That is mostly good for liquidity at that moment, but it concentrates risk too: a disruption around 4 p.m. on a month-end day would hit an unusually large share of activity at once. The post also shows how much market structure can depend on a private firm's operational choice - a single index provider moving its clock by an hour visibly reshaped the trading day.