“We are closed due to annual leave and will be back in week 23”.

“The number of Covid-19 cases was far lower in week 27 than in weeks 25 and 26”.

“The marketing department wants the project to be finalised by week 42”.

If you’ve ever read (or heard) a sentence like any of the above in Danish and found yourself cursing in frustration and grasping for your smartphone to google “what date is week 23”, you’re not alone.

The use of week numbers to refer to points in time – either in the past or future, but usually within the current year or beginning of the next one – is common in some European countries, and Denmark has embraced it with particular gusto since its official introduction in the 1970s.

In Anglophone countries including the United Kingdom and United States, the convention is not used and weeks are more likely to be referred to loosely as the “second week in July”. If a specific week needs to be given, it might be written down as a range of dates or something like “the week commencing Monday July 18th”.

As such, the use of week numbers can be exasperating to people not used to them, because they are difficult to connect to an actual date and therefore don’t seem to give any kind of useful reference point. They require the extra step of referring to a calendar to look up a date which could have just been given in the first place.

At the same time, Danes often seem to instinctively be aware of the week number they’re currently in, the exact date of an earlier week number, and how far into the future a given week number might be.

Below, we look at why week numbers are commonly used in Denmark and where the practice comes from.

How does it work?

Denmark’s calendar system designates as “week 1” the first week in the year which includes four or more days of the new year (in other words, four January days with no more than three still in December).

Another way of putting this is: the first week in which Thursday is in January is week 1.

This means that the number of weeks in a year can vary, because 52 multiplied by 7 is 364. As such, week 53 sometimes makes an appearance at the tail end of the Danish calendar.

It follows that week 1 can start in the old year and week 53 can include days in January. It’s probably a good thing that most people are still on their Christmas holidays at this time of the year.

Why does Denmark use this system?

Denmark introduced the numbering system for weeks on January 1st 1973 (a Monday), in accordance with an international standard, ISO 8601. The country began considering Monday, rather than Sunday, as the first day of the week at this point.

Week numbering was used in Denmark prior to 1973, but as documented in a 2018 Kristeligt Dagblad article, it was less widespread and not standardised. This was partly due to the convention of Sunday as the first day of the week.

“Up to now every country, so to say, has used the same rule for distributing the weeks, namely that Sunday was the first day of the week; whereas different rules were used for the numbering of the weeks,” a contemporary Danish calendar from 1973 states.

“With the increasing usage of week numbers, for example for fixing delivery deadlines, these irregular rules give cause to misunderstandings regarding international trade,” it continues.

As such, an increasing need for efficient international trade meant Denmark switched from the custom of weeks beginning on a Sunday – which has its roots in religion – to modernising its calendar and weekly numbering system for the benefit of international trade.

It’s perhaps not surprising that this happened in 1973, the year after Denmark joined the European Community – later the EU. 

Some countries – like the United States – still designate Sunday as the first day of the week in calendars. This is also the case in Israel, where Sunday is a regular weekday.

In conclusion, there doesn’t appear to be anything specific to Danish culture that would make week numbers popular, although you could argue its relatively secular nature made it easier to adopt the change from weeks starting on Sundays and irregular numbers.

The introduction of standardised week numbers to make international trade smoother also seems to have been readily accepted in Denmark, a small country reliant on strong imports and exports.

Because week numbers are important in international logistics, it’s easy to imagine them quickly becoming established at businesses in Denmark – where freight giant Maersk is the biggest company in the country.

With workplaces using them, the people working there need to keep track of them, and this means they’re more likely to be able recall which week number they’re in than someone from a country where these are not used.

The result of nearly 50 years of thinking about dates in this way? It’s easier to answer quickly when the receptionist at your GP asks if you can come for your next follow-up check in “week 13”.

How can I stop being frustrated by it?

I don’t have all the answers to this, but one way of making it easier to look up week numbers (and one Danes sometimes use themselves and have suggested to me) is to change the settings on your phone calendar to display them.

On an iPhone, this can be done in the Settings->Calendar section by switching on “Week Numbers”. On Android devices, you can use the settings within the calendar app to show week numbers.

The same calendar but with week numbers displayed.