Arizona and Sonora: the Same Time, Every Day of the Year
Arizona's southern neighbor, the Mexican state of Sonora, keeps exactly the same clock as Arizona — UTC−7, all year, with no daylight saving time on either side. Phoenix, Tucson, Nogales, Hermosillo, and Guaymas always read the same minute. For the busiest trade corridor in the region, there is simply no time difference to think about.
That's rarer than it sounds. Most US–Mexico border pairs drift an hour apart for part of the year. Arizona–Sonora is the exception because both sides independently decided the clock change wasn't worth it.
How Both Sides Ended Up Clock-Fixed
- Arizona opted out of US daylight saving time in 1968 — an extra hour of evening sun is a liability in the desert. The full story is in our DST guide.
- Sonora briefly observed Mexican DST in the late 1990s, then opted out
in 1998 — explicitly to stay synchronized with Arizona, its dominant trading partner.
Sonora even has its own IANA time zone,
America/Hermosillo, to record the difference from the rest of Mexico.
Mexico Abolished DST in 2022 — Mostly
In October 2022, Mexico ended daylight saving time nationwide. Most of the country, including Mexico City, now stays on standard time permanently — the same philosophy Arizona adopted half a century earlier.
The exception runs along the US border: municipalities in the border strip (Tijuana, Mexicali, Ciudad Juárez, Nuevo Laredo, Reynosa, Matamoros, and others) still observe US-schedule DST so they stay aligned with their twin cities across the line. Sonora needs no such arrangement — it already matches Arizona without moving anything.
Arizona vs Mexican Cities, at a Glance
| Place | Offset | Difference from Arizona |
|---|---|---|
| Sonora (Hermosillo, Nogales MX, Guaymas) | UTC−7 year-round | None, ever |
| Mexico City / most of Mexico | UTC−6 year-round | 1 hour ahead of Arizona, year-round |
| Baja California (Tijuana, Mexicali) | Pacific, with US DST | Same as AZ in summer; 1 hour behind in winter |
| Ciudad Juárez (border strip) | Mountain, with US DST | 1 hour ahead in summer; same as AZ in winter |
Since neither Arizona nor Mexico City changes its clocks anymore, that one-hour gap is now constant — a 9:00 AM call from Phoenix always reaches Mexico City at 10:00 AM, in any month. Our home page converter includes both Mexico City and Sonora if you want to check a specific time.
Practical Notes for the Border
- Crossing at Nogales: no clock change in either direction, ever.
- Scheduling with suppliers in Hermosillo or Guaymas: treat them as local — business hours line up exactly with Phoenix and Tucson.
- Phone clocks near the border can occasionally grab a tower on the wrong side and jump an hour in areas outside Sonora (e.g., near Baja California in winter) — the Arizona–Sonora line itself is safe.