This is a simple question, but one I've never seen a definitive answer for:

In the majority of the world that has postal codes, is it safe to assume that given a postal code, there is only one time zone associated with that postal code?

Or alternately, even if it it's not safe in principle, has there ever been an actual case where one postal code spanned two or more time zones?

  • 2
    this question is off topic here... but I am curious to know the answer – TheCatWhisperer Oct 5 '17 at 18:48
  • Happy to move it, or have it moved, but I couldn't decide where to put the question. Stack Overflow seemed equally off-topic. – user802500 Oct 5 '17 at 18:52
  • 3
    In countries with daylight saving time, one postal code area may have different timezones at different points of time. I don't have a concrete example, but some postal codes are not geographic but have special uses, e.g. denote an organizational entity. That entity may be present in multiple time zones. You'll probably be able to find an example for military mail postcodes. – amon Oct 5 '17 at 19:10
  • 2
    Have to vote to close this as off-topic, but I will say that if you have the polygons for time zones and postal zones, that question becomes very easy to answer. Also note that some postal zones don't equate to physical locations. – Blrfl Oct 5 '17 at 19:19
  • I think this is a great question - is it really off-topic here? This essentially questions a fairly typical assumption in software engineering. Would it be a better fit if it were framed a little bit differently, e.g. "is it future-proof to store postcodes and timezones in the same DBMS table?". Though I've noticed that similar questions have been decided to be off-topic before and I certainly get your point. – Bengt Oct 5 '17 at 21:03

I believe the answer is no although I think it is more about usage. There can be multiple time zones in a single zip. As an example look at the rules for military mail on usps (https://pe.usps.com/text/pub28/28c2_010.htm). There are a few specific zips that include many different time zones around the world.


It depends on how essential it is you get an accurate timezone, and whether the user can configure their timezone. There are indeed various cities in the world that have multiple timezones. Its safe to assume that there are also postal codes that use different timezones.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.