Numerous resources indicate that preferences regarding the inclusion of leading zeroes in clocks (08:42 vs. 8:42 in 24-hr clocks; 03:42 p.m. vs. 3:42 p.m. in 12-hr clocks) may be unique to individual markets / countries. Yet it is frustratingly hard to locate comprehensive resources on what these preferences are on a per-country basis.

My question is -- what are these preferences by country (for major markets)? Do comprehensive resources exist on these preferences?

Evidence Such Preferences Exist

A table by Aaron Marcus, indicates that there are preferences in leading zeroes in clock display that are societal preferences often on a per-time bases:

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(This table is shown in "Human-Computer Interaction: Design Issues, Solutions, and Applications" : "Chapter 2: Global/Intercultural User Interface Design" (author: Aaron Marcus) pg 31 and "Human Computer Interaction Handbook: Fundamnetals, Evolving Technologies, and Emerging Applications 3rd Ed." :"Chapter 15: Globalization, Localization, and Cross-Cultural User-Interface Design" (author: Aaron Marcus and Emilie W. Gould) pg 354)

This suggests that there is indeed such a preference on a per country basis and that it is perhaps independent from preference of 12-hour vs. 24-hour clock. (And hence that it may be desirable to localize whether to pad with leading zeros or not pad regardless of whether the mode is 12-hr or 24-hr.)

Further evidence that differences in padding preferences are determinable by country is found in a Wikipedia article "Date and Time Notations in Europe" which asserts:

Just as with the date format, leading zeros seem to be less common in [clocks in] Germany than in Austria and Switzerland...

(Analyzing the non-English source is challenging as it is no longer available from the linked page.)

Current Approaches

I see in general the topic is treated by the coding community in a couple of ways:

  • Leave it up to the user

    This approach is seen in Oracle's Javascript API and Microsoft's SQL Server Data Analysis Expression (DAX) formulas API which include for 24-hour clocks the ability to either use the leading zero or not use it.

    My feeling is that this flexibility is arguably a good thing for certain applications, but the decided downside is it gives no attempt to give the developer default behavior respecting local market preferences, hence leaving it to developers to try to formulate their own localizations.

    Note: some standards adopt this sort of laissez-faire perspective as well -- Unix's strptime standard (v2, (c) 1997) for instance proclaims that leading zeros are permitted but not required.

  • Force the user to do what we think is best

    One of the more popular standards for 24-hour clocks in Europe is ISO 8601 which mandates padding with leading zeroes to two digits.

    The disadvantage here (in my view) is that market preferences may be ignored. For devices with no pre-digital clock feature -- the phone for instance -- this may be somewhat less of a problem. For other devices including transportation consoles (aircraft, cars, etc.) that had clocks in the pre-digital face this in my view is more problematic as you're not only disregarding the colloquial local preference, you're likely disregarding the behavior of your target in the pre-digital era.

    This is often justified by the argument that it is "more logical" to display a leading zero to cue the user that the time they're seeing is a 24-hour time and not an ambiguous time in 12-hr format with the "A.M."/"P.M." identifier missing. However, even if the assumption that the leading zero helps users identify a 24-hour clock is generally correct, it fails to fix other ambiguity problems such as those observed when the clock reads 11 or 12.

What Do Users in Specific Countries Prefer?

My preference would be to default to the localized preference in my UI, but I need help locating comprehensive resources discussing preference padding with leading zeros by country.

In general a paradigm of UI design is to tailor your UI per the conventions of your target audience. The classic instance of this is whether to use a 12 hour depiction of time versus a 24 hour one. Various tables have been proposed for on a per-country basis which is most appropriate.

The passages above a similar country-based preference table could be formulated for leading zero preferences -- the question is has it?

I'm not looking to be told "just use ISO 8601" because while that may be some professionals' perspective, it does not answer the question topic of providing resources to determine preference by country for padding w/ leading zeros.

If such a compilation does not exist, alternatively it would be valid to propose here based on individual resources indicating preference for a specific country.


I removed the anecdotal about clock faces in OS X as it was pointed out it was discussing more of an unusual use of leading zeroes in a 12-hr clock.

  • 1
    Being in the UK, I'd argue that we are generally a 12 hour am/pm culture and the only contact with 24 hour clocks is generally train timetables. An error I've hit a few times are people reading 16.00 as 6pm / 17.00 as 7pm etc. We aren't very skilled at it because we don't generally deal with it.
    – PhillipW
    Commented Jan 25, 2017 at 20:31
  • Would you say most 12 hour clocks from local retailers follow the convention of not padding with zeros when the time is single digits? Commented Jan 25, 2017 at 22:54
  • 1
    I actually looked at opening hours online for some of the big supermarket chains and the ones I looked at (Tescos and Sainsburys ) are actually using 24 hour - with leading zeros. However I'd have doubts about whether us locals find that format easy to use - particularly one of the stores listing 06.00 - 00.00 opening hours. ( 00.00 requires thinking about and therefore breaks the 'don't make me think' rule )
    – PhillipW
    Commented Jan 25, 2017 at 23:22
  • Intriguing, thanks for sharing your research and perspective... I'm thinking I'll try to do something similar to confirm whether the assertion that Germany tends not to include the leading zero also is accurate. Commented Jan 25, 2017 at 23:34
  • A common approach in Japan is to use the 24 hour system and continue with it after the 24 hour passed if it is relevant. For example, if a film starts at 23 and finishes at 01 of the next day, the cinema schedule will note 23:00-25:00. This is actually quite useful, as where I live a 24 hour limit doesn't help in these situations (it can even become more extreme, with a film listed on Friday to start at 01:00 when is actually on Saturday at 01:00. Friday at 25h fixes this issue.)
    – Alvaro
    Commented Jan 25, 2017 at 23:38

1 Answer 1


Pad the 24-hour clocks; don't pad the 12-hour clocks.

The provided table seems to indicate that a 24-hour clock has leading zeros while a 12-hour clock has an AM/PM indicator.

I think you misspoke when referencing the forum with the irritated UK user--I read that as the user was irritated when they saw a leading zero on a 12-hour clock. This would actually provide evidence to support that 12-hour clocks should not have leading zeros (also, it's a rather weak source, being from 2008 with only one response, so this shouldn't independently sway your decision too much...).

I live in the US where most civilians use 12-hour format but our military uses 24-hour time. My understanding of the two major time formats is that the leading zero helps to indicate that the time is in 24-hour format and it's not just missing the AM/PM indicator.

Given these sources, I think the easiest and clearest treatment is to let the user select the 12- or 24-hour clock, present all times with the colon separator (as opposed to the dot as referenced in the wiki page), and pad only the 24-hour clocks with zeros.

  • Doesn't the commentary re: "leading zeros seem to be less common in [clocks in] Germany than in Austria and Switzerland" suggest some 24-hour markets prefer not to pad with zeros? I'm revising based on your observation of that source, but the fact still remains that some academic sources are suggesting localized preferences within the subset of countries with 24-hour clocks, right? (see: discussions in the Wikipedia article on time in Europe and the book chapters by Marcus) Commented Jan 25, 2017 at 22:47
  • Also I thought U.S. military time's exclusion of the spacing character : would be the primary factor identifying that it's not a 12-hour clock? Wouldn't that do a better job identifying that it is not a 12-hour clock, as it would not only discern the single digit cases, but 11 and 12 as well? Commented Jan 25, 2017 at 22:51
  • @JasonR.Mick (to your first comment) Hmm, perhaps. I guess I was reading that commentary you mentioned as being in contrast to Germany's more traditional dot notation. Commented Jan 25, 2017 at 22:53
  • @JasonR.Mick This is indeed more complicated of an issue than it appears at first glance. Perhaps my answer is over-simplified, but then again, it would probably be much more straightforward to implement. In terms of making a solution that generally works for everyone, I would imagine most users being okay with a 24-hour clock showing a leading zero. To present the option to the user for displaying a leading zero seems a bit overkill (unless displaying time is central to your use case) as most users wouldn't care (this is an assumption, but it feels safe to make). Commented Jan 25, 2017 at 23:03
  • You're probably right... however, it seems automatic localization of whether or not to display the zeros could be done if there was a body of knowledge on the preferences by country. It could perhaps localize base upon the preference of the country in which your last product update occurred or in which the product was sold. Commented Jan 25, 2017 at 23:08

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