EST will still mean UTC-5 in Canada though, at least this winter. Would that have to become CEST (*shudders*)? I think TZDB has done that with AEST, which Australia calls EST.
If TZDB continues to call them both EST, this will just shift the problem to downstream users, because the real world will come up with distinct names. On Wed, 15 Jul 2026 at 20:36, James Bellaire via tz <[email protected]> wrote: > On 7/15/2026 7:44 AM, Brooks Harris via tz wrote: > > I remember that discussion, although I hadn't followed all the > > comments. It's not helping me feel comfortable. :-) > > H.R. 139 is clear in the changes being made to the laws controlling time > zones in the US. The names of the existing zones are not being changed. > We will still have Atlantic standard time, eastern standard time, > central standard time, mountain standard time, Pacific standard time, > Alaska standard time, Hawaii-Aleutian standard time, Samoa standard time > and Chamorro standard time. The proposed adjustment changes the offset > from UTC, not the names so the discussion over name changes is moot. > AST, EST, CST, MST, PST, AKST, HST, SST and ChST still work. The > colloquial names for the zones (such as "Eastern Time" or "Central > Time") still work. They still refer to standard time, whatever time that > is for the date specified. > > As long as downstream programs respect the change in the offset they > should not break. Downstream programs that for some reason hard code > "EST" as -05 instead of using tzData have created their own problems. > This change in this form was first proposed in 2018 so that has been > plenty of warning for downstream programs that EST could not always > equal -05. > > The zones in tzData can be updated to reflect what the clocks on the > wall say. Puerto Rico, Arizona, Hawaii, Samoa and Guam (and any other > current no DST area I missed) will need to make their intention clear so > their zone in tzData is not changed. It will be strange to see > America/Phoenix define MST as -07 and America/Denver define MST as -06. > Perhaps Arizona can be convinced to change the name of their zone to > "Pacific Standard Time"? (Although that will affect Creston BC Canada. > As will any name change in PR will affect eastern Quebec.) > > Of course, the bill still needs to pass the Senate. So we are borrowing > problems from the future. As long as the senate sets an effective date > of November 7 2027 before passing the bill there will be time to adjust. > > Best wishes to all the programmers who are looking at their code and > hoping the Senate does not pass the bill (no change is the easiest > outcome). > >
