# ZIP Code Timezone Calculator

> zip code timezone calculator that maps any US ZIP code to its time zone, current local time, and UTC offset instantly. Free, runs in your browser, no signup.

- **Canonical URL:** https://boringtoolskit.com/zip-timezone-calculator/
- **Category:** Converters
- **Evidence level:** authored-methodology
- **Reviewed:** July 26, 2026
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

The calculator looks up your 5-digit ZIP code in a USPS ZIP table where every row carries a latitude, longitude, county, and IANA timezone name. It reports the zone plus its UTC offset for the selected date, computed as local time = UTC time + offset, with the offset rising by one hour during daylight saving for zones that observe it.

## Worked example

ZIP 00601 resolves to Adjuntas, Puerto Rico (FIPS 72001, latitude 18.18004, longitude -66.75218) in the America/Puerto_Rico zone. That zone keeps Atlantic Standard Time at UTC-4 all year with no daylight shift, so at 16:00 UTC the local time is 16 - 4 = 12:00 PM AST on any date. For contrast, ZIP 33101 in Miami sits in America/New_York: in December it reads 16 - 5 = 11:00 AM EST, and in July it reads 16 - 4 = 12:00 PM EDT.

## Assumptions

- Each ZIP code resolves to one primary timezone taken from the center coordinates of its delivery area; ZIP codes that straddle a boundary follow the side holding most of the population.
- Daylight saving offsets follow the current IANA tzdata rules, with US daylight saving running from the second Sunday in March to the first Sunday in November for participating zones.
- The ZIP table reflects the active USPS ZIP code list at the time it was built, so very new, retired, or PO-box-only records may not return a result.

## Common questions

### How many timezones cover US ZIP codes?

The 50 states, DC, and the territories span 10 base zones: Eastern, Central, Mountain (with a separate no-daylight-saving Arizona zone), Pacific, Alaska, Hawaii-Aleutian, Atlantic, Chamorro, and Samoa time. The IANA names behind them include America/New_York, America/Chicago, America/Denver, America/Phoenix, America/Los_Angeles, America/Anchorage, Pacific/Honolulu, America/Puerto_Rico, Pacific/Guam, and Pacific/Pago_Pago, plus a few county-level variants in Indiana, Kentucky, and North Dakota.

### Does the result change with daylight saving time?

Yes. Enter a date and the calculator returns the offset in force on that date, so New York ZIPs show UTC-5 (EST) in January and UTC-4 (EDT) in July. Zones without daylight saving, including Arizona, Hawaii, Puerto Rico, Guam, and American Samoa, keep a constant offset every day of the year.

### Why does my ZIP code show a different city or county than I expected?

USPS assigns each ZIP code to a single delivery processing point, and the primary city name in the table is that point's city, not necessarily your mailing address city. The county and coordinates refer to the center of the delivery area, which can sit miles from any given address inside the ZIP.

## Related tools

- /timezone-converter/

## Sources

- [Time Zone Database (tzdata)](https://www.iana.org/time-zones)
- [ZIP Code Lookup API](https://www.usps.com/business/web-tools-apis/zip-code-lookup-api.htm)
- [Postal Code Downloads](https://download.geonames.org/export/zip/)

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