Standard Time, Time Zones & Daylight Saving Time

The rules that tell Americans when the clock changes are federal law, not just custom. Congress sets the national daylight-saving framework in the Uniform Time Act, while the U.S. Department of Transportation controls time-zone boundaries and decides whether proposed state or local boundary changes serve the convenience of commerce. Under current law, most of the country still changes clocks twice a year. In 2026, daylight saving time began on March 8, 2026 and will end on November 1, 2026. States may opt out of daylight saving time and remain on standard time year-round, but they generally may not adopt year-round daylight saving time without Congress changing federal law.

Current Law (2026)

Legal Authority

• 15 U.S.C. § 260a — National daylight saving time rule, including state exemptions
• 15 U.S.C. §§ 261-264 — Federal standard time zones, including the core continental and noncontiguous zones
• 15 U.S.C. § 265 — Procedures for changing time-zone boundaries
• 15 U.S.C. §§ 266-267 — Publication and legal-effect provisions tied to zone changes
• 49 CFR Part 71 — DOT regulations describing standard time-zone boundaries

How It Works

Federal time law has a two-layer structure: the Uniform Time Act establishes the national time zones, and the Sunshine Protection Act (as amended) overlays the seasonal daylight saving rules on top of them. A state can stay on standard time year-round by invoking the opt-out provision, but the underlying time zone boundary still comes from federal law and DOT's boundary regulations — states don't have unilateral authority to relocate themselves into a different zone. DOT's time-zone boundary review process is oriented toward the "convenience of commerce": when a community or state petitions to change zone boundaries, DOT evaluates commuting patterns, broadcast markets, transportation links, and cross-border business ties rather than treating it as a purely local preference question. The asymmetry in state authority is a persistent source of public confusion: rejecting daylight saving time (staying on standard time permanently) is explicitly authorized under current federal law and requires only a state legislative opt-out. Keeping permanent daylight saving time would require a change to the federal statute — a state cannot simply declare permanent DST on its own. Arizona's patchwork illustrates this well: most of the state doesn't observe DST, but the Navajo Nation generally does, producing different clock times within a single state depending on whose land you're standing on.

Key Numbers

• How many Americans are affected: approximately 300 million people in 47 states + D.C. change their clocks twice a year; Hawaii and most of Arizona do not observe DST; Puerto Rico, Guam, the U.S. Virgin Islands, and American Samoa also stay on standard time year-round
• Economic disruption: academic studies estimate the twice-yearly clock change costs the U.S. economy approximately $434 million/year in lost productivity, accident costs, and health effects (various peer-reviewed estimates); a 2016 JPMorgan study estimated a measurable productivity drop in the week following the spring-forward transition
• Health impact: peer-reviewed studies show heart attack rates increase approximately 24% in the week after the spring clock change (University of Michigan, published in Open Heart, 2014); car accident fatalities increase approximately 6% the Monday after spring forward (Colorado State University study); workplace injuries spike similarly
• States with contingent permanent-DST laws: 19+ states have enacted laws that would switch to permanent DST if Congress changes federal law — but those laws cannot take effect without federal action
• Senate vote history: the Sunshine Protection Act passed the Senate unanimously in March 2022 — one of the rare 100-0 Senate votes — but the House never brought it to a floor vote before the 117th Congress expired; the pattern repeated in the 118th Congress; S. 29 is the 119th Congress version

How It Affects You

If you manage a team or run a business: The spring clock change causes measurable productivity disruption — the Monday after "spring forward" consistently shows higher workplace accident rates, more scheduling errors, and lower cognitive performance in research studies. For shift-work operations, the November fallback creates an overtime complication: an overnight worker whose shift spans the 2:00 a.m. clock-fall-back is legally owed pay for the extra hour, even though the clock appears to show only an 8-hour shift. Payroll software that doesn't handle this correctly underpays workers. For businesses billing by the hour, calendar software that doesn't properly handle the DST boundary can create double-billing or missed-billing errors on exactly one night per year.

If you live in or near Arizona: Arizona's non-DST status creates one of the most complex timekeeping situations in the U.S. In a single afternoon's drive, you can cross three different time realities: Mountain Standard Time (most of Arizona), Navajo Nation Daylight Time (the Navajo Reservation, which observes DST even though it sits inside Arizona), and Mountain Standard Time again (the Hopi Reservation, which does not observe DST and is entirely surrounded by Navajo land). This patchwork affects court filing deadlines, medical appointment scheduling, broadcast programming, and commerce across these boundaries. If you have clients, patients, or business partners on or near the reservations, building in a time-verification step is essential from March through November.

If your state legislature has passed a contingent permanent-DST bill: More than 19 states have enacted laws that automatically take effect if Congress permits permanent DST — but those laws are dormant until federal action. The Sunshine Protection Act (S. 29 in the 119th Congress) would remove the federal bottleneck. If it passes, your state law would snap into effect, and the clocks would stop changing permanently. The problem: a state that switches to permanent DST before its neighbors would create new border confusion — your morning meeting with a colleague in the adjacent state could shift by an hour for half the year. Congress's delay partly reflects the coordination complexity, not just inertia.

If you travel internationally: The U.S. and Europe don't change their clocks on the same date. The U.S. springs forward in mid-March; most of Europe doesn't follow until late March. During that 2-3 week window, the usual time difference between U.S. cities and European cities shifts by one hour — which means your standing Thursday call at 3 p.m. Eastern might now land at an unexpected time for your London counterpart. Airlines, international Zoom calls, and transatlantic shipping schedules all have to navigate this temporary misalignment twice a year (once in spring, once in fall). International travel itineraries built months in advance are particularly vulnerable to this gap.

State Variations

• Hawaii stays on standard time year-round
• Most of Arizona stays on standard time year-round, while the Navajo Nation generally observes DST
• Puerto Rico, Guam, the U.S. Virgin Islands, and American Samoa do not observe DST
• Some states have passed resolutions or contingent statutes favoring permanent DST, but those laws cannot take full effect unless Congress changes federal law

Implementing Regulations & Guidance

• 49 CFR Part 71 — DOT time-zone boundary regulations
• DOT Time Zone Boundary Guidance — Explains the process for state and local requests to move county or municipal boundaries between time zones
• NIST / time.gov guidance — Publishes the annual DST start and end dates used across federal systems

Pending Legislation (119th Congress)

• S. 29 — Sunshine Protection Act of 2025: would move the country toward permanent daylight saving time
• H.R. 1630: would let states choose year-round daylight saving time without waiting for a nationwide switch
• H.R. 7378 — Daylight Act of 2026: would revisit the federal clock-change framework from a different direction, reflecting the continuing split between permanent-DST and permanent-standard-time camps

Recent Developments

The Sunshine Protection Act's repeated near-miss is the dominant story. The Senate passed S. 623 unanimously in March 2022 — a 100-0 vote that made permanent DST seem imminent — but the House never scheduled a floor vote before the 117th Congress ended. The 118th Congress saw the same bill reintroduced and the same outcome: Senate interest, House inaction. S. 29 in the 119th Congress follows the same pattern as of April 2026. The bill has unusual bipartisan support, but it's caught between competing concerns: airlines and sports leagues want more evening light and predictable schedules; religious communities note that permanent DST means very late sunrises in December (after 9 a.m. in some northern cities); international businesses worry about coordination complexity if the U.S. moves alone while Europe stays on its own schedule.

The medical research consensus has shifted — and it conflicts with public preference. Major medical organizations including the American Academy of Sleep Medicine and the American Heart Association have issued formal position statements recommending Congress move to permanent standard time, not permanent daylight saving time. Their argument: standard time better aligns with the body's circadian clock (sunrise should precede work hours), and the evidence linking poor circadian alignment to cardiovascular disease, metabolic disorders, and mental health problems supports permanent standard time as the healthier choice. This creates a politically awkward situation: polls consistently show the public prefers permanent DST (people like evening light after work), but the experts recommend the opposite. Congress has had difficulty threading this needle.

European precedent has complicated U.S. deliberations. The EU voted in 2019 to end seasonal clock changes and allow member states to choose their permanent time. But implementation has been repeatedly delayed because if neighboring countries choose different options, border regions end up with a confusing one-hour gap. That concern applies directly to the U.S.-Canada border — Canada is watching U.S. legislative action before deciding on its own clock policy, and the close economic integration between the two countries makes unilateral U.S. action more complicated than it looks.