The local time that happens twice
When the clocks go back, an hour repeats. Two different instants have the same wall clock, and every library silently picks one.
2026-11-01 01:30 · America/New_York → UTC
Sun, 2026-11-01, 01:30 in America/New_York is Sun, 2026-11-01, 05:30 in UTC — but that local time happens twice.
2026-11-01T05:30:00.000Z
From
America/New_York
Sun, 2026-11-01, 01:30
UTC−04:00 · EDT
To
UTC
Sun, 2026-11-01, 05:30
UTC+00:00 · UTC
Both possible instants
- 2026-11-01T05:30:00.000Z
- 2026-11-01T06:30:00.000Z
What to watch for
This will bite you
That local time happens twice
01:30 on 2026-11-01 occurs twice in America/New_York, because the clock went back over it. Both candidate instants are listed, and they are a real hour apart. Every library silently picks one; which one it picks is rarely documented.
Fix: Say which occurrence you mean by giving the UTC offset explicitly, or store the instant rather than the local time.
Note
UTC does not observe daylight saving
UTC keeps the same offset all year, so its clocks never change. If the other zone does observe it, the gap between them shifts twice a year even though nothing changes on this side.
Upcoming clock changes
America/New_York
2026-11-01T06:00:14.062Z
Clocks fall back an hour: the wall clock returns to 01:00, so that hour happens twice.
UTC−04:00 → UTC−05:00 (EDT → EST)
2027-03-14T07:00:00.000Z
Clocks jump forward an hour: 01:59 is followed by 03:00, and the times in between never happen.
UTC−05:00 → UTC−04:00 (EST → EDT)
UTC
No clock changes — this zone keeps one offset all year.
Convert your own time
Use the form on the home page, or call the API or MCP server. This page is also available as markdown.