1918
DST timeline
Daylight saving time in United States has 3 recorded changes on record, spanning 1918–2007. The earliest documented event is the adoption in 1918: Federal daylight saving time began under the Standard Time Act, alongside federal standard time zones. The most recent is the modification in 2007: The current US DST season took effect, running from the second Sunday in March to the first Sunday in November. As of the latest data, United States is shown as "Regional" in our daylight saving tracker, which is the practical takeaway for anyone scheduling calls, travel, or deliveries against this region today.
Each entry records a distinct daylight saving milestone for United States. An adoption marks the year clocks first began shifting; an abolition marks the year the country stopped changing them and settled on a single year-round offset; a modification covers changes to the start or end dates, the size of the shift, or which regions take part; and a reform vote records a legislative or parliamentary decision that may not yet be in force. Years reflect when the change took effect, not when it was announced, so a 2019 vote and a later effective date can both appear.
Daylight saving rules change more often than most people expect, and historical offsets are exactly the detail that breaks date math for past timestamps, travel records, and historical scheduling. If you only need today’s behaviour for United States, the current-status link above is the fastest answer; if you are reconstructing a past date or comparing several countries, the full timeline and the linked sources below give you the authoritative record.