On week numbering in the United States

Continuing the chatter in my earlier discussion of why January 1 is being reported as the last week of the previous year.

Commenter Smithers notes a few things, which I will use as my springboard.

Seriously though, USA, why can't you let a week that's in two years at once just be one week? Also FirstDayOfWeek=Sunday?? It's called the week*end*, it comes at the *end* of the week.

As I noted in my inline comment: Like a rope or stick or soccer pitch, a week has two ends. There's the front end (Sunday) and the back end (Saturday). One interpretation of the word "end" is is "not the beginning"; another is "extremity".

The reality is that the term "end" in "weekend" doesn't actually mean "end". The term "weekend" refers to any day that is not a day of work. Hence phrases like "long weekend".

And then there are the religious-historical reasons why Saturday is the seventh day of the week, which in turn makes Sunday the first day of the week.

But I'm really here to talk about week numbers.

Basically, in the United States, we don't use them. So go ahead, Europe, use your fancy week numbering schemes, with the rule of four or the rule of Thursday or the rule of St. Benedict. (I may have made up that last one.)

Since the United States doesn't use week numbers to any significant extent, the definitions are chosen to align with how people talk in casual conversation: "Week 1" is the first week of the year, and it begins on January 1. The weeks are then numbered consecutively, with each subsequent week starting in on Sunday.

This numbering scheme means that most of the time, Week 1 is a partial week, and so is Week 53.

Wk Su Mo Tu We Th Fr Sa
December 2015
49 1 2 3 4 5
50 6 7 8 9 10 11 12
51 13 14 15 16 17 18 19
52 20 21 22 23 24 25 26
53 27 28 29 30 31
January 2016
1 1 2
2 3 4 5 6 7 8 9
3 10 11 12 13 14 15 16
4 17 18 19 20 21 22 23
5 24 25 26 27 28 29 30
6 31

I should emphasize that you will not see a calendar in the United States that looks like this, because nobody cares about week numbers.

This simple numbering scheme aligns with how people talk about weeks. "It'll be done in the last week of 2015" means "It'll be done some time between December 27 and December 31 of 2015." Nobody expects "the last week of 2015" to extend into 2016.

Similarly, if somebody says, "It'll be ready in the first week of 2016," then if it is ready on December 27, 2015, it will be considered to have completed ahead of schedule. Nobody expects "the first week of 2016" to extend into 2015.

In the United States, the conventional calendar milestones are not weeks; they are months. Things are scheduled for "the first week of November" or "the middle of October" or "the end of April." And the definition of "the first week of the month" is "Starting on the first day of the month, and extending until the first Saturday of the month." Similarly, "the last week of the month" is "Starting on the last Sunday of the month, and extending until the last day of the month."

I remember when I visited Sweden, I saw a notice that said something like "Opening in Week 23!" That meant nothing to me. I didn't know what week number were were in currently, so I couldn't calculate how many more weeks before the building opened. I also had no sense of whether Week 23 was springtime or summertime or autumn. The weeks may as well have been assigned colors or shapes.

Comments (51)
  1. Medinoc says:

    Quite frankly we practically don’t use week numbers in France either. I always assumed it was only added on some year calendars to “look smart”.

    1. Matteo Italia says:

      FWIW, I have never seen week numbers here in Italy.

    2. smf says:

      We don’t use them much in the UK either. Our tax year starts on the 6th of April, and many businesses run their financial year the same to make things easier but you can start your financial year whenever you like. So when week numbers are used, they aren’t necessarily the standard ones anyway.

      1. dirk gently says:

        Not in use in Poland either.

    3. AP² says:

      Same here in Portugal. The small company I work for started using them internally for task tracking purposes, and everyone has to lookup what week we’re actually in, since it’s not used anywhere else.

  2. I had to read this post to even notice that my desktop calendar displays week numbers indeed. Here in Spain nobody uses them in daily life. I once had to create some reports that matched week numbers stored in database; client was completely unable to explain how they calculate them.

  3. bickerdyke says:

    Well, over here (Germany), no one expects anything done between Christmas and New Year, as this is “between the years”. So I guess that’s how we get around the problem with the partial week…

    And while I’m using week numbers heavily at the office, I have hardly seen them in public live, as your opening notice.

  4. ken lubar says:

    My observation over the years is that accountants always think in weeks ending while marketers think weeks beginning. I guess it has something to do with financial types wanting the real numbers and marketers being optimistic. And then there is always the scheduling confusion of whether “moving a date back” means it is happening sooner or later.

    1. Daniel Neely says:

      For the first few years I worked there my employer’s pay week (and scheduling week for labor planning) ran from Friday-Thursday. the explanation I had for why this was done was that it reduced the amount of unpaid overtime salary employees ended up stuck with from either staying late working getting a deliverable out (I never saw a bias towards Friday for those dates on anything I worked on though), and by splitting a full calendar week of on site work in half if let people count the travel to the customer site on Sunday night and return home on Friday night or Saturday morning in two different weeks. That let people who knew they’d be making a several hour hour trip to the customer leave early on Friday since they knew they’d get the rest of the 40 chargeable hours we still needed to get (yay contracting for the US Govt as salaried) in per week, and could use the hours spent on the return trip to cover leaving early one the following week.

      OTOH it confused the hell out of new hires, and even for people knew how it worked, figuring out that work week March ran from Friday Feb 26 to Thursday Mar 31 meant looking at a calendar, and a few years after I started there they scrapped it and went to a conventional Sunday to Saturday work week; with partial weeks at the start/end of the fiscal year as the only anomoly.

      1. cheong00 says:

        [the explanation I had for why this was done was that it reduced the amount of unpaid overtime salary employees ended up stuck with from either staying late working getting a deliverable out (I never saw a bias towards Friday for those dates on anything I worked on though)]

        FYI, the amount of OT payment on Saturday and Sunday (if there is any) should be greater than weekday, so I agree with your employer that this can “reduce the amount of unpaid overtime salary employees ended up stuck with”.

  5. MarkT says:

    At my US-based company, WW1 is the Sun-Sat week containing January 1, so the last few days of December are in WW1. There is a WW53 every few years when Jan1 is on a Friday or Saturday.

  6. Boris says:


    “Swedes have a custom of sometimes mentioning week numbers instead of dates – for instance, the Sportlov (Sports break) in Stockholm is always in week nine of each year, regardless of what specific dates are involved. Other parts of Sweden have their week of Sportlov in weeks 6-10. Vacation may be referred to as “This year, my summer vacation is week 25 to 29”, which usually means somewhere around mid June to mid July. However, Swedes think it is a convenient way of keeping track of when things happen, as dates may vary even if the week number is the same. In Swedish calendars, week numbers are always noted.”

    1. Jakob Eriksson says:

      “However, Swedes think it is a convenient way of keeping track of when things happen, as dates may vary even if the week number is the same.”

      Exactly – this is the reason. That said, a Swede myself, I have to *always* look in a calendar to see which week it is. I do know, however, that there are about 52 weeks in year so I do know roughly what part of the year is meant.

      I am hardly the only week-impaired person in Sweden, or this site would not exist: http://vecka.nu/

  7. MC says:

    Interestingly in the UK I’ve only started using them fairly recently and that’s with the introduction of TFS and Agile sprint board. A sprint will be held on Week 22+23 of the year, the next one will be weeks 24+25 etc. Maybe that’s some configuration option someone in the organisation has chosen.

  8. Tom says:

    Is it possible to create a custom culture with the Lord of the Rings calendar. 12 months of exactly 30 days each with those in between days not belonging to any Month? :)

    1. Boris says:

      I’d be fine with 13 months of 28 days each, plus one special day.

      1. Tom says:

        The Druid / menstrual cycle / lunar based on. Let’s do that too

        1. Boris says:

          I think the easiest approach would be to resurrect Sextilis and put it before September. The summer months of June, July and August tend to merge in my mind, so another one wouldn’t really make a difference. All birthdays and holidays would keep their day-of-month numbers for backwards compatibility, except that those exceeding 28 would be celebrated on the 28th. The last, special day of the year could be called New Year’s Eve, to be preceded in leap years by Leap Day. (I just made this up intuitively, having read about proposals for reform a long time ago, so I’m sure that most of this isn’t that original.)

    2. RonBass says:

      Sounds like the French Revolutionary Calendar.

  9. Zhila says:

    In a blog post focused on date/time concepts posted on the Friday before the US “celebrates” the beginning of Daylights Savings Time, the related PSA appears to be missing.

  10. Anders Munch says:

    “Basically, in the United States, we don’t use them. ”

    Following that, you are in no position to argue that the US system is better. If the US system is so bad that you don’t even use it yourselves, then you’re not going to convince me that it’s better than the ISO standard system.

    1. We don’t use week numbers, but we do say “the first week of” and “the last week of”, and the numbering system is consistent with how those phrases are used.

  11. My desk calendar at work has week numbers on, but we actually do care about them: navigation chart and data corrections and notices to mariners are identified by their week number. Most of our own data updates to ships also use the week number to identify them as well (except for things that update more frequently)

    Although this is probably a bit esoteric.

  12. Florian S. says:

    Quote: And the definition of “the first week of the month” is “Starting on the first day of the month, and extending until the first Saturday of the month.”

    According to this definition: What if the first day of a month is a Saturday? Will it be a one-day-week, or an eight-day week?

    Quote: The term “weekend” refers to any day that is not a day of work.

    This definition is a bit ambivalent. First: Usually, Sunday is not a day of work as well, so at least to me (I’m from Germany) it feels weird that in the US the Saturday is considered the “weekend”, and not Sunday (and when people talk about the weekend around here, they usually mean both Saturday and Sunday). Second: A holiday is not a day of work as well, and it can happen at any day of a week. Now, would you call a holiday that happens on Tuesday a “weekend”? And does it make Wednesday the start of a new week?

    Questions, questions… :)

    1. If the first day of the month is a Saturday, then, yes, it’s a one-day week. I again emphasize that all of these “rules” are informal. The term “weekend” strictly refers to Saturday and Sunday, but if there is a holiday on Monday or Friday, then honorary weekend status is given to the holiday as well. Honorary weekend status is frequently given if Tuesday or Thursday is a holiday, on the theory that most people will not come to work on the corresponding Monday or Friday. It’s not clear why you think that the placement of holidays affects when weeks begin and end.

    2. Wear says:

      Weekend isn’t the same as the end of the week. If Sunday is the start of the week then Saturday is the end of the week but Saturday and Sunday together are the weekend. If you have a holiday in the middle of the week you could call it a weekend but it wouldn’t be the end of the week.

      Words are weird.

  13. Dave says:

    At least the “rule of Thursday” has the benefit of a standard, ISO 8601. Let’s all agree to pick the same arbitrary-but-reasonable rule so we stop misunderstanding each other.

  14. Indeed, we often do talk about week numbers in Sweden. Hence, I am very happy that Microsoft Outlook has an option to display these. I am still using Windows 7 (because I love Windows Media Center), and I am sometimes annoyed by the lack of week numbering in the taskbar calendar.

  15. Nico says:

    Aside from being ambiguous, week numbers seem to be redundant as well. Why say “Opening Week 12” when you can just as easily say “March 27th” or “Week of March 27th” or “third week of March”?

    Of course we could always go full-Psychlo and use day numbers for everything. “Opening on Day 89!”

  16. Martin says:

    Oddly appropriate post for the day. Today I implemented functionality to determine which is the first week of a given month for reporting purposes. The rule I had to work with was: “A week is reported in a month if the last business day of that week is in that month”.

  17. vibes says:

    No, the end of a time unit is the last part of it. That’s why you say “this weekend”, not “this pair of weekends”. Religious or circular etymological reasoning does nothing to change that. And despite that anecdote from Sweden, week numbers are not casually used in daily life in Europe – nobody here can off the top of their head say what is the current week number. It is a handy shortcut to use when planning (and calculating) future activities, though. And it requires all parties involved to have a calendar at hand for reference.

  18. jgh says:

    Wednesday is the middle of the week. That’s why you have mid-week football on Wednesday, that’s why it’s called mid-week-day in German, that’s why the current affairs program after the 6am-9am news is called MidWeek. If Wednesday is midweek, then the week must logically therefore run Sunday-to-Saturday. The weekend is the bit that’s at the ends of the week. You need two bookends to make a functional bookshelf. Besides, doing it any other way looks horribly lopsided and makes it harder to use for its function. If you think “what’s the day next Wednesday?” it’s easy to glance at a calendar and skim down the middle to find it, or move to the side to Tuesday/Thursday/etc.
    is much more logical, straightforward and conducive to reading than

    1. Alex Cohn says:

      In Hebrew, there is no word for “Sunday”: it’s simply called “the first day”. Same applies to the rest of the days of the week, except Sabbath. This naming convention can be traced back to Gen:1.1.

  19. Neil says:

    As opposed to Week 54, which is always a partial week.

  20. Scott Conger says:

    I have a feeling some Microsoft customer will cite this blog post when submitting an Excel bug report.

  21. James Sutherland says:

    On a national level, we don’t use them in the UK either. My university does, though – with at least two completely incompatible numbering systems in use!

    Each week of teaching is numbered – for example, we’re about to start “semester 2, week 10”. However, there’s a two week break for Easter – so week 12 is actually four weeks from now, thanks to the two week gap between weeks 11 and 12. Apart from the gaps, this is quite logical: we start in week 1, have a review half way through in week 7, finish teaching in week 12 (then have exams, coursework etc after that). There’s even a published calendar listing which day each week starts.

    Meanwhile, Finance consider this to be something like week 29 of the financial year – and require all their forms to be completed accordingly. (Pragmatic outcome: take a rough guess which week it is now, see which date their spreadsheet auto-populates itself with, then adjust accordingly. No, they don’t let you enter dates directly: that would be too user-friendly.) Thanks to gaps, converting isn’t just a matter of adding/subtracting a constant number, nor does there seem to be any documentation for their numbering system except trial and error on their forms…

    Outside the university itself, nobody would refer to a date by week number – almost always a month, or sometimes an event (“by year-end”, “before Christmas”) or (usually in financial circles) by quarter. The Swedish system seems quite bizarre from here: do they use these week numbers instead of months, or some sort of mixture?

    1. gdalsnes says:

      “The Swedish system”
      It’s hardly Swedish. Here is a list of countries required to adopt EN 28601 (ISO 8601), UK is actually among them:

      1. Boris says:

        James Sutherland clearly meant the cultural practice of using week numbers on an everyday basis, not the standard by which they’re calculated.

    2. Andreas says:

      > The Swedish system seems quite bizarre from here: do they use these week numbers instead of months, or some sort of mixture?

      Well, it is, I guess. It’s sometimes convenient but most of the time I find it just as confusing as Raymond did. I generally don’t keep track of week numbers so I dislike it when stores put up signs like that, better just say a specific date. When it comes to week numbers, I know that where I live we have the spring break in week 7 and all daycare/kindergartens close down during the weeks 28-31 so that’s when I’ll have my summer vacation. Don’t ask me what dates those weeks are because I don’t know. I know they’re typically in July. If you ask me what week it is now, I wouldn’t know.

      I guess there are other people who are more into time-tracking and who probably will know exactly what week it is now and the dates of any random week. But in my experience, though, it seems most people are just winging it: E.g. if I’m in a meeting and the manager says something should be done by week 16, I typically ask when that is, which has the (IMHO) hilarious consequence that the manager (who so confidently sprouts week numbers) starts flipping through his/her calendar to find the exact dates.

  22. Engywuck says:

    > the definition of “the first week of the month” is “Starting on the first day of the month, and extending until the first Saturday of the month.”

    So “first week of april” this year has only two days? I would have thought “first week of april” was 4th to 10th this year, but then I’m german :-) (and it’s KW14 btw)

    1. Ray Koopa says:

      I’d expect the first week of month X to be whatever week housing the day 1 of month X. I never heard someone handling it differently, and I’m from Germany too. (You probably mean CW rather than KW for “calendar week”, btw ;3)

  23. Ray Koopa says:

    I’m from Germany, and while some typical gray office calendars show the week numbers, noone really cares about using them. I totally agree to your explanations about how week numbers are chosen.

  24. Gunnar Dalsnes says:

    “It’ll be done in the last week of 2015″ means “It’ll be done some time between December 27 and December 31 of 2015.”
    Weird. Aren’t weeks 7 days? But if you should pretend weeks are only 5 days, wouldn’t it make more sense to include only working days: “It’ll be done some time between December 25 and December 29 of 2015.”

    1. Most years begin and end with a partial week. (Another way of looking at it is that the week that straddles a year boundary has split jurisdiction; the first part belongs to the previous year, and the second part belongs to the following year.) If you mean the last seven-day week, then you would say “It’ll be done in the last full week of 2015.”

  25. DWalker says:

    “And then there are the religious-historical reasons why Saturday is the seventh day of the week, which in turn makes Sunday the first day of the week.

    I thought that “on the seventh day, God rested” and that was Sunday. No matter; that’s from a history that was written well after the time…

  26. EMB says:

    Dates are complicated, lets do math… Wait, what?

  27. BZ says:

    In my experience (in the US) while some people say things like “first week of April” it’s better not to because it’s ambiguous. If I heard that, My first guess would be the first 7 days (or 5 weekdays if in a business context) of April. I would always say “week of April 3” or even better, “week starting April 3”. Much like some people say “week and a half”. What does that mean 10 days? 11 days? 10.5 days? Each of these is easier to say and write than “week and a half”.

    1. A week and a half is intentionally imprecise. I generally take it to mean anywhere from 9 to 12 days, and I tend to snap it to weekends. So if today is Tuesday, then both the Saturday and Sunday after next would be a week and a half from now, and both the Saturday and Sunday before the previous one would be a week and a half ago.

  28. Jan says:

    I’m from Europe (Netherlands) and tbh, I think the week numbering thing is a bit odd. I agree with your logic of calling it the first or last week of a month instead of calling it Week 23. I also never know when it is. Of course, it’s somewhere before July because 53/2=26 is somewhere around July. Still, everyone around me uses it and I always have to look up the current week number.

  29. Random832 says:

    I suspect that some people would consider “the last week of 2015″ to start on the 25th no matter what day it falls on, and others would consider it to mean the last full week and change, at least of any year in which “and change” is too small (e.g. Dec 24+ 2017, Dec 23+ 2018), with various definitions of “too small”.

    Basically, the split may not extend “across” years, but it also may not get to be the “first” or “last” week of the year.

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