In our app you can select a start date and the app calculates the end date (we're talking about subscriptions here). This is from midnight to midnight, so the actual points in time are, for example:

2020-05-18 00:00:00 to 2020-05-25 00:00:00

So the period starts on the midnight of the 18th, runs all day long, then a few more days, then stops on the midnight between the 24th and the 25th. 24th is included in the interval; 25th is not. But the timestamp itself is the midnight of the 25th.

So how to best communicate this to the user? Some options:

  • 25th May, 2020 - matches the timestamp, but can be misleading. People might thing that the 25th is included.
  • 24th May, 2020 - still can be misleading. Someone might think that the 24th is NOT included. But this is my personal favorite.
  • 24th May, 2020 (inclusive) - wordy? Is this clear enough?
  • 24th May, 2020, 23:59:59 - Dunno, looks kinda ugly to me, but it is kinda accurate....

Or maybe something else entirely?

2 Answers 2


NIST says the 23:59:59 solution or.... 24:00:00 on the 24th


"To avoid ambiguity, specification of an event as occurring on a particular day at 11:59 p.m. or 12:01 a.m. is a good idea, especially legal documents such as contracts and insurance policies. Another option would be to use 24-hour clock, using the designation of 0000 to refer to midnight at the beginning of a given day (or date) and 2400 to designate the end of a given day (or date)."

Either way it's a good idea to avoid mentioning the 25th if someone then has to perform some mental logic to backtrack to the 24th


What do the users say? The absolute best thing to do is ask users in a usability test.

If you can't ask users…

Starts  Midnight 18 May 2020
Ends    Midnight 24 May 2020

seems like a straightforward way of doing it that most people will understand. Even if the numbers aren't exactly the same in the background it doesn't matter. People understand what this means.

Exactly how it's displayed depends on the rest of the UI though for context.

  • This seems like the most confusing option of all. Does it refer to the midnight at the start of the day or at the end?
    – user1686
    Commented May 30, 2020 at 19:32
  • You're confusing me 🙂 Commented May 30, 2020 at 22:50
  • Is it a cultural thing to think of midnight as the start of the day? If someone asked me to meet them at midnight on 18 May, I would be there on the night of the 18th. It wouldn't occur to me that it could be the night before. Commented May 30, 2020 at 22:51
  • 1
    Possibly? Your example is disambiguated by the fact that people more often stay late until midnight than wake up near midnight, but that doesn't help in all cases. Checking my local web sites and articles, it seems that "midnight of a specific date" is commonly used both ways, it's a 50/50 as to whether it indicates the beginning or the end of that day. Always great when the same government policy is stated to end at "midnight of May 31st" and "midnight of June 1st"... (That said, notice that in 24-hour scale, 00:00 is at the beginning, with the rarely-used 24:00 indicating the end.)
    – user1686
    Commented May 31, 2020 at 7:50

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