You might have heard what they say about the Scandinavian languages: That they're so closely related that a Dane can just speak his own language and be understood by a Norwegian or a Swede and that pretty much everyone understands everything?
Well, the reality is a little more complicated. The Scandinavian languages are close. But a Dane speaking Danish like he would with his fellow countrymen would be difficult to grasp for a Swede who hasn't got a lot of exposure to Danish.
This doesn't mean that Scandinavians switch to English when communicating, though. I've found that most Swedes, Danes, and Norwegians will go to great lengths to communicate in their local languages rather than speaking English despite most people being able to speak English at a pretty high level.
Each part has to adapt, however. When Danes speak slowly, try and adapt their vocabulary and, if speaking about numbers, try to say them like a Swede would, communication is possible.
Demographics And Regions Play A Role
The mutual intelligibility of Swedish and Danish also depends on geography and demographics.
Some regions of Denmark tend to speak Danish dialects that are further removed from Swedish than "standard" Danish, such as Southern Jutlandic. Interestingly, the Southern Jutlandic dialect seems to have a lot in common with the Low-Germanic languages and dialects spoken south of the border, but also Frisian and Dutch.
Other Danish dialects have had a lot more exposure to Swedish historically. Many people from Zealand, the island where Copenhagen is situated, have grown up listening to Swedish radio and watching Swedish television, which makes it easier for them to adapt their Danish to be a little easier to decipher for a Swede.
On the other side of the water, in Southern Sweden, or Scania, Danish comprehension has improved over the last few decades. The construction of the Øresund (or Öresund) bridge, connecting Copenhagen with the Scanian city of Malmö has meant that thousands of Swedes and Danes are now crossing the borders every day, to go study or work on the other side.
It's not uncommon at all to meet Swedish waiters and staff, working in various businesses, restaurants, and tourist attractions in Copenhagen as well as students in various universities and learning institutions.
This free movement across the borders has meant that especially the Swedish inhabitants of Scania have gotten used to listening to Danish. This is, however, to a large extent a regional thing, and Swedes from the North and Danes from the rest of Denmark might find it slightly more complicated to understand one another (even though switching to English is still, rarely a thing.)
Listening And Reading Are Two Very Different Things
Another thing to take into consideration is how a Swede would be exposed to Danish. The biggest difference between the two languages is in how they're pronounced, and spoken Danish is difficult to understand, not only for Swedes but for... Everyone.
When comparing Danish, Norwegian, and Swedish, the Danish language stands out as the most inconsistent, pronunciation-wise. The three languages have common roots and they initially (historically) all sounded pretty much the same, but Danish, especially since the second half of the 20th century, has become more and more muffled and unclear.
Today, the Danish language is written with a lot of silent letters or syllables that only very slightly modify the pronunciation of a word, where they would represent a very distinct sound in Swedish. Because of this strange, muffled way of pronouncing the language, many Swedes compare the Danish language to someone trying to speak Swedish with a huge, hot potato stuffed in their mouths.
We, Danes, have a lot of clever come-backs to that one, but I'm not going to elaborate on those here!
Where Danish pronunciation is very different from Swedish, the two languages do look alike in their written form. This means that there's a huge difference in terms of spoken and written intelligibility, and generally, Swedes would have no trouble understanding Danish writing, except for a few words that are different here and there, and a couple of false friends that might be confusing at first.
Conclusion: Do Swedes Understand Danish?
Popular Scandinavian television series have spread the rumor internationally, that Swedes and Danes can just speak their own language and understand one another without making any kind of effort.
The reality is a little more complicated.
Danish and Swedish are two very closely related languages, but they have some important differences in how they're pronounced, and generally, a Swede wouldn't necessarily understand Danish if he or she hadn't had a lot of previous exposure to the language.
It doesn't take a long time to get used to how the other Scandinavians speak, however, and learning how to understand another Scandinavian language doesn't really feel like language learning at all!