The Weeks When New York and London Disagree About Clocks
Posted: Thu Oct 29, 2026 3:40 am
The Weeks When New York and London Disagree About Clocks
Scenario: a trader in a time zone fixed at UTC plus 1, with no daylight saving, tracks US data released at 8:30 a.m. Eastern Time. The release shifts on their clock during the year, and the shift does not align with London's clock change.
In winter, Eastern Time is UTC minus 5, so 8:30 is 13:30 UTC. For the UTC plus 1 trader, that is 14:30.
After the United States moves its clocks forward, on the second Sunday of March, Eastern Time is UTC minus 4, so 8:30 is 12:30 UTC. The trader sees it at 13:30.
London moves its clocks forward on the last Sunday of March. London local time becomes UTC plus 1. The release now appears at 13:30 London time, and still 13:30 for the trader, since neither the release in UTC nor the trader's clock changed.
For about two to three weeks in March, between the two changes, the release appears at 12:30 London time, one hour earlier than the usual 13:30. The same mismatch appears briefly in the autumn, when the United Kingdom changes before the United States.
Consequence: any rule defined in London local time, such as "avoid trading in the hour before US data," needs updating. A rule in UTC does not.
Use UTC for all session and event rules, and convert once to your clock.
Exercise: list the dates this year when the clock changes occur, and mark them in your calendar.
Scenario: a trader in a time zone fixed at UTC plus 1, with no daylight saving, tracks US data released at 8:30 a.m. Eastern Time. The release shifts on their clock during the year, and the shift does not align with London's clock change.
In winter, Eastern Time is UTC minus 5, so 8:30 is 13:30 UTC. For the UTC plus 1 trader, that is 14:30.
After the United States moves its clocks forward, on the second Sunday of March, Eastern Time is UTC minus 4, so 8:30 is 12:30 UTC. The trader sees it at 13:30.
London moves its clocks forward on the last Sunday of March. London local time becomes UTC plus 1. The release now appears at 13:30 London time, and still 13:30 for the trader, since neither the release in UTC nor the trader's clock changed.
For about two to three weeks in March, between the two changes, the release appears at 12:30 London time, one hour earlier than the usual 13:30. The same mismatch appears briefly in the autumn, when the United Kingdom changes before the United States.
Consequence: any rule defined in London local time, such as "avoid trading in the hour before US data," needs updating. A rule in UTC does not.
Use UTC for all session and event rules, and convert once to your clock.
Exercise: list the dates this year when the clock changes occur, and mark them in your calendar.