ZIP to Timezone

Finding the correct timezone for a US ZIP code is essential for scheduling meetings across regions, calculating delivery windows, sending time-sensitive notifications, and displaying local times in applications. Our ZIP to Timezone tool returns the IANA timezone identifier, current UTC offset, standard name, and daylight saving time (DST) status for any 5-digit US ZIP code — covering all 50 states, DC, territories, and military postal codes.

The Four Mainland US Timezones and Their ZIP Code Coverage

The contiguous United States spans four standard timezones. The Eastern Time Zone (ET) covers roughly 16,000+ ZIP codes from Maine to Florida and west to Indiana and Michigan, observed as EST (UTC-5) in winter and EDT (UTC-4) in summer. The Central Time Zone (CT) covers approximately 13,000 ZIP codes from the Upper Midwest through Texas and Louisiana, observed as CST (UTC-6) in winter and CDT (UTC-5) in summer. The Mountain Time Zone (MT) covers the Rocky Mountain states with approximately 5,000 ZIP codes, observed as MST (UTC-7) in winter and MDT (UTC-6) in summer. The Pacific Time Zone (PT) covers the West Coast with approximately 7,000 ZIP codes, observed as PST (UTC-8) in winter and PDT (UTC-7) in summer.

Beyond the continental US, Alaska (AKT/AKDT, UTC-9/-8) and Hawaii (HST, UTC-10, no DST) add two more zones. US territories span additional offsets: Guam and Northern Mariana Islands use ChST (UTC+10), American Samoa uses SST (UTC-11), and Puerto Rico and US Virgin Islands use AST (UTC-4, no DST).

IANA Timezone IDs vs. Abbreviations

Timezone abbreviations like EST, CST, MST, PST are widely understood in the US context but are globally ambiguous — CST is used for Central Standard Time (US), China Standard Time, Cuba Standard Time, and Central Summer Time (Australia). For applications handling international users or storing timestamps in databases, always use IANA timezone database identifiers (also called tz database or Olson database identifiers). US IANA IDs include: America/New_York (ET), America/Chicago (CT), America/Denver (MT), America/Los_Angeles (PT), America/Anchorage (AKT), Pacific/Honolulu (HST). These IDs are understood by all major programming languages, databases, and date/time libraries.

Daylight Saving Time: The Exception States

The United States observes DST from the second Sunday in March to the first Sunday in November — with two major exceptions. Arizona (excluding the Navajo Nation) does not observe DST and permanently uses MST (UTC-7). All Arizona ZIP codes except those within the Navajo Nation reservation always return MST regardless of time of year. Hawaii does not observe DST and permanently uses HST (UTC-10). US territories (Puerto Rico, Guam, Virgin Islands, American Samoa, Northern Mariana Islands) also do not observe DST.

Timezone Boundaries and ZIP Code Edge Cases

Timezone boundaries in the US generally follow state lines, but in several states the boundary runs through the state, creating splits. Indiana ZIP codes fall in both ET and CT depending on county — most of the state is ET, but southwestern Indiana (around Evansville) is CT. Tennessee is split between ET (east) and CT (west). Kentucky is mostly ET but western counties are CT. Florida Panhandle west of the Apalachicola River is CT while the rest of Florida is ET. Our tool uses per-ZIP-code timezone assignments to correctly handle all these edge cases.

Using ZIP Timezone Data in Applications

The most common application use cases for ZIP-to-timezone: displaying local time for a user based on their ZIP code in their profile; scheduling communications (emails, SMS, phone calls) during appropriate local hours; calculating estimated delivery windows in local time; validating time-sensitive form submissions (e.g., "order before 5 PM local time for same-day processing"); and converting timestamps stored in UTC to the user local time for display.

A robust pattern: store all timestamps in UTC in your database, resolve the user's IANA timezone from their ZIP code, and use the IANA ID with a date/time library (Luxon, Day.js with timezone plugin, Python's pytz or zoneinfo) to display UTC times in local time. This approach correctly handles DST transitions without any special-casing.

ZIP Timezone for Scheduling and Business Hours

Call center teams use ZIP timezone data to determine when to call prospects — a lead in a 213 area code in Los Angeles should not be called at 8 AM when a rep in New York is starting their day, because it would be 5 AM Pacific time. Automated systems that send appointment reminders, shipping notifications, and promotional messages use ZIP timezone to localize the send time to each recipient local morning or afternoon, improving open rates and reducing opt-outs.

Military ZIP Codes and Timezone

Military APO (Army Post Office) and FPO (Fleet Post Office) ZIP codes are assigned to three military postal regions: APO AE for Europe/Middle East/Africa, APO AP for the Pacific, and APO AA for the Americas. These do not correspond to a specific timezone in the traditional sense because they route mail to overseas locations that may be in any timezone. Our tool returns the military designation for these ZIPs rather than a civilian timezone.