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Why do Danes insist on using week numbers instead of dates?

It can be frustrating having to regularly check which date is meant by a given week number, but there’s method in the numerical merry-go-round.

Why do Danes insist on using week numbers instead of dates?
A calendar on which week numbers are given higher prominence than actual dates. Photo by Behnam Norouzi on Unsplash

“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.

An iPhone calendar

The same calendar but with week numbers displayed.

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For members


Five classic Danish cakes you need to try

You may have tasted kanelsnegle, romkugler and tebirkes, but have you tried these hard-to-find cakes yet? If not, you're missing out.

Five classic Danish cakes you need to try


Literally translating as “Napoleon’s hat”, this pastry, which consists of a ball of marzipan baked on top of a shortbread biscuit, folded in the shape of a tricorne hat and dipped in dark chocolate, dates all the way back to 1856.

In the early 19th century, Denmark sided with France in the Napoleonic wars, which proved to be a bad idea: the UK bombed Copenhagen, stole the Danes’ entire naval fleet and Denmark was forced to concede Norway to Sweden following the Treaty of Kiel in 1814.

At least the Danes got a pastry out of it: and the triangular marzipan-flavoured pastries – somewhere between a cake and a biscuit – are still popular in Denmark as a great afternoon treat with a cup of coffee.

napoleonshat should not be confused with the equally delicious napoleonskage, which is a cake similar to a French millefeuille, a dessert consisting of two layers of puff pastry filled with cream and raspberry jam and glazed with white or brown icing.


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Despite the name, you’ll be pleased to know that a kartoffelkage (literally: “potato cake”) does not include potatoes, with the cake instead getting its name due to its resemblance to a freshly-dug potato.

Kartoffelkager are a classic Danish cream cake or flødeskumskage, consisting of choux pastry (vandbakkelse) filled with crème pâtissière, known as kagecreme or “cake cream” in Danish.

They are then topped with a disc of marzipan and dusted with cocoa powder, giving them the appearance of a muddy potato fresh out of the ground.

Best eaten as fresh as possible and using a fork, it’s easy to understand how this cake, with the bitter cocoa powder, smooth vanilla-flavoured kagecreme and obligatory marzipan has become a classic.


The kajkage. Photo: Kjersti Hjelmen/NF/Ritzau Scanpix

From one classic to another, the kajkage is an essential Danish cake which you’re unlikely to find in hip Copenhagen bakeries.

This cake, shaped like a frog and covered in lime-green marzipan, is easier to find outside of Denmark’s larger cities, where you’re likely to see it in the shop windows of smaller local bakeries who aren’t too snobbish to stock the less-than-elegant pastry.

Originally referred to as a simple frøkage (frog cake), legend has it that an enterprising baker in Holstebro in western Jutland started marketing the cake under the name kajkage in the 1980s, after Kaj the frog, from popular children’s TV series Kaj og Andrea (Kaj and Andrea).

kajkage consists of a macaron-style base, known as a mazarinbunde in Danish, where marzipan (yes, the Danes love marzipan if you haven’t already figured that out), is mixed with egg, flour, sugar and butter and baked into a thin cake.

This is then cut out into rounds and topped with a layer of raspberry jam, then a layer of buttercream, which is then covered in green marzipan. A slice is then cut into the marzipan for the frog’s mouth with an optional red marzipan tongue, and two googly eyes are piped on to finish the cake.

Understandably popular with children, you should try a kajkage at least once in your life – if only to impress any Danes you know from more rural areas of Denmark with your local cake knowledge.


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Another classic, medaljer (medals) are the first cake on this list which do not include marzipan.

They have fallen somewhat out of fashion in recent years, but join kartoffelkager as one of the essential flødekager, which became popular at the turn of the 20th century when new technological advances made it possible to keep dairy products cold.

Medaljer, unlike kajkager, are extremely elegant, consisting of two discs of shortcrust pastry filled with a ring of either whipped cream or crème pâtissière, filled with some sort of compote or jam, usually a sour flavour to cut through the rich cream like raspberry or apple. They are then topped with icing or dark chocolate, and some sort of decoration, like a piped blob of cream or some fresh fruit.

Despite their often simple appearance, medaljer are surprisingly difficult to make, as the texture of the cream and compote filling must be stiff enough to ensure it can hold up the biscuit on top, while not being over-whipped.


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The final cake on this list, invented in western Sjælland at the beginning of the 1900s, is a gåsebryst (goose breast).

It gets its name from the domed shape and texture of the white marzipan topping. When marzipan was still made and rolled-out by hand, it was difficult to get it completely smooth, with the texture ending up similar to the feathers on a goose’s breast.

gåsebryst is a somewhat old-fashioned cake which you are more likely to find at a konditor than a standard bakery.

It consists of a base made of sponge cake or puff pastry, spread with some kind of fruit compote or jam (usually raspberry, more traditionally prune), and a dome of cream and kagecreme, formed into a long log. The log is then topped with uncoloured marzipan and drizzled with chocolate, then sliced into individual slices so the cross-section of the cake is visible.