Civil Time AtlasIANA time zone data

tzdata rule group

US

Active or recent rule group · 40 represented zones

A rule group describes recurring clock changes. It is not itself a place or an IANA time-zone identifier.

First rule
1918
Last rule
2026 or later
Rule entries
13
Source files
northamerica

Notes from the time database

Context for this rule

These source notes are preserved from tzdata. They help explain a rule’s period, without adding claims beyond the source.

Where it appears

Zones using US

Only historically distinct canonical zones from this atlas are listed.

Original rule fields

Recorded rule entries

Structured directly from tzdata’s Rule lines.

FromToTypeInOnAtSave
19181919-MarlastSun2:001:00
19181919-OctlastSun2:000
1942only-Feb92:001:00
1945only-Aug1423:00u1:00
1945only-Sep302:000
19672006-OctlastSun2:000
19671973-AprlastSun2:001:00
1974only-Jan62:001:00
1975only-FeblastSun2:001:00
19761986-AprlastSun2:001:00
19872006-AprSun>=12:001:00
2007max-MarSun>=82:001:00
2007max-NovSun>=12:000