Tillykke med fødselsdagen.

Yes. It is the standard, natural phrase Danes use to congratulate someone on their birthday.

A few very common versions are:

• Tillykke med fødselsdagen = the full, standard phrase
• Tillykke! = shorter, very common in speech and messages
• Hjertelig tillykke = warmer, a bit more heartfelt
• Stort tillykke = big congratulations, also common in messages

So if you learn just one birthday phrase, Tillykke med fødselsdagen is a very good choice.

Because Danish says it as congratulations with/on the birthday, not literally happy birthday.

The phrase pattern is:

• Tillykke med ... = congratulations on/with ...

You can use this with many occasions:

• Tillykke med jobbet = Congratulations on the job
• Tillykke med eksamen = Congratulations on the exam
• Tillykke med brylluppet = Congratulations on the wedding

So med is the normal preposition after tillykke.

Because Danish usually uses the definite form here: the birthday.

• fødselsdag = birthday
• fødselsdagen = the birthday

In this expression, Danish normally says:

• Tillykke med fødselsdagen

That is simply the idiomatic form. English says Happy birthday, but Danish prefers Congratulations on the birthday.

You may sometimes hear shorter or more casual variations in special contexts, but fødselsdagen is the standard form in this phrase.

Yes, absolutely. Tillykke! is very common and sounds natural.

People often use:

• Tillykke!
• Hjertelig tillykke!
• Stort tillykke!

If it is already clear that it is someone’s birthday, Tillykke! is often enough by itself, especially:

• in conversation
• in a text message
• on social media
• when giving a card or gift

A rough guide is:

• Tillykke ≈ ti-LY-guh
• med ≈ mel or soft með, depending on pronunciation style
• fødselsdagen ≈ FUR-selz-dai-en or FUR-sels-dain

A few useful notes:

• y in Tillykke is not like English y. It is a rounded vowel that English does not really have.
• ø in fødselsdagen is also a vowel English does not have.
• The d in med and dagen is often soft, not a hard English d.
• In natural speech, Danes often reduce sounds, so the phrase can sound smoother and less fully pronounced than the spelling suggests.

If you want a simple learner-friendly target, aim for something like:

ti-LY-guh mel FUR-sels-dai-en

It will not be perfect, but it will be understandable.

In modern Danish, tillykke is best learned as a fixed congratulatory expression.

You do not need to analyze it too much at first. The most useful thing is to remember:

• Tillykke! = Congratulations!
• Tillykke med ... = Congratulations on ...

Historically, it is related to lykke, meaning luck or fortune, but for a learner it is easiest to treat tillykke as a set phrase rather than trying to build it word by word.

Normally, no. The natural order is:

• Tillykke med fødselsdagen

That is the standard fixed phrase.

You would not normally say:

• Med fødselsdagen tillykke
• Fødselsdagen tillykke
• Tillykke fødselsdagen

Those sound wrong or unnatural in ordinary Danish.

So it is best to memorize the phrase exactly as:

Tillykke med fødselsdagen

Only if normal spelling rules require it.

In Danish, nouns are not capitalized the way they are in German. So normally you write:

• Tillykke med fødselsdagen.

At the start of a sentence, Tillykke is capitalized because it is the first word, not because it is a special noun.

In a card or message, people may also write:

• Tillykke med fødselsdagen!

The exclamation mark is very common and sounds friendly.

It is neutral and works in almost any situation.

You can say it to:

• a friend
• a family member
• a colleague
• a neighbor
• someone older than you
• someone you do not know very well

If you want to sound warmer or more personal, you can add something:

• Hjertelig tillykke med fødselsdagen = Heartfelt congratulations on your birthday
• Stort tillykke med fødselsdagen = Big congratulations on your birthday

But the basic phrase by itself is completely appropriate in both casual and polite situations.

Usually it is said on the birthday itself, or very close to it.

If you say it before the day, it can sound a little early unless the context makes that clear. In that case, people might instead say something like:

• Tillykke på forhånd = congratulations in advance

And if it is late:

• Forsinket tillykke med fødselsdagen = belated happy birthday

So Tillykke med fødselsdagen is most natural on the birthday itself.

Yes, a few.

Common ones include:

• Tillykke med fødselsdagen = standard full phrase
• Tillykke! = short and common
• Hjertelig tillykke med fødselsdagen = warmer, more heartfelt
• Stort tillykke med fødselsdagen = very common in writing and messages

You may also hear:

• Tillykke med dagen

This is less specific literally, but in the right context it can mean something like happy birthday / congratulations on your day. Still, if you want the safest and clearest phrase, use:

Tillykke med fødselsdagen