Hvis jeg havde fridag på mandag, ville jeg spise frokost med min mor.

It is a hypothetical conditional sentence, similar to English:

If I had Monday off, I would eat lunch with my mother.

The speaker is not stating a fact. They are talking about an imagined situation.

A very common Danish pattern is:

Hvis + past tense ..., ville + infinitive ...

That works much like the English If ... had ..., would ... pattern.

Because Danish uses the past tense in the hvis-clause to express an unreal or hypothetical situation.

So:

• Hvis jeg har fridag på mandag ... = if I have Monday off ...
  This sounds like a real possibility or something still open.
• Hvis jeg havde fridag på mandag ... = if I had Monday off ...
  This sounds hypothetical or contrary to the actual situation.

This is very similar to English:

• If I have Monday off ...
• If I had Monday off ...

Even though the meaning refers to the present or future, Danish often uses past tense for this kind of unreality.

Because Danish main clauses follow the verb-second rule.

The sentence begins with the subordinate clause:

Hvis jeg havde fridag på mandag

That whole clause takes the first position in the sentence. Then, in the main clause, the finite verb must come next:

... ville jeg spise frokost med min mor.

So the word order becomes:

1. subordinate clause
2. finite verb
3. subject
4. rest of the sentence

That is why you get:

Hvis jeg havde fridag på mandag, ville jeg ...

and not:

Hvis jeg havde fridag på mandag, jeg ville ...

Yes, in this sentence ville means would.

But ville can be tricky, because it can also be the past tense of vil, which often means want to or sometimes will depending on context.

For example:

• Jeg vil spise. = I want to eat / I will eat.
• Jeg ville spise. can mean:
  • I wanted to eat in a past context, or
  • I would eat in a conditional context.

Here, because of the Hvis ... havde ... structure, ville is clearly conditional: would.

This is because Danish often uses certain nouns in fixed expressions without an article.

Here, have fridag means to have a day off.

So:

• jeg har fridag = I have a day off / I’m off work
• jeg havde fridag = I had / would have a day off

That said, many Danes would more naturally say:

Hvis jeg havde fri på mandag ...

Using fri is often more idiomatic in everyday speech than fridag in this sentence.

You may also hear:

have en fridag

if the speaker wants to emphasize one day off as a countable thing.

It is understandable, but many native speakers would probably say:

Hvis jeg havde fri på mandag, ville jeg spise frokost med min mor.

Why?

• have fri is a very common everyday expression for be off / have time off
• have fridag is possible, but it can sound a bit more noun-based or less natural in casual speech
• have en fridag is also possible if you want to stress a day off

So the sentence is fine, but havde fri is often the more idiomatic choice.

På mandag means on Monday, usually referring to the coming Monday in context.

Examples:

• Vi ses på mandag. = See you on Monday.
• Jeg arbejder på mandag. = I’m working on Monday.

The preposition på is very common with days of the week when referring to a specific day.

For an English speaker, it helps to think of it as matching on in on Monday, even though Danish uses på rather than a direct equivalent of English on in all cases.

Sometimes yes, but på mandag is the most natural choice here.

Danish can use a bare weekday in some contexts, especially in schedules, headings, short notes, or very compact speech. But in a full sentence like this, på mandag sounds more normal.

So:

• Jeg kommer mandag. = possible
• Jeg kommer på mandag. = very natural

In your sentence, på mandag is the expected phrasing.

Because meals in Danish often behave like they do in English: they appear without an article after spise.

So:

• spise morgenmad = eat breakfast
• spise frokost = eat lunch
• spise aftensmad = eat dinner

This is just like English eat lunch, not usually eat a lunch.

You could say en frokost in a more specific context, but in ordinary usage spise frokost is the standard expression.

Because Danish possessive pronouns normally come before the noun:

• min mor = my mother
• min far = my father
• min ven = my friend

So med min mor simply means with my mother.

English speakers sometimes wonder whether family words can stand alone more often, but in this sentence, min mor is the normal way to say it.

Yes, the comma is standard here.

The sentence starts with a subordinate clause:

Hvis jeg havde fridag på mandag

and then moves into the main clause:

ville jeg spise frokost med min mor

In standard written Danish, these are separated by a comma:

Hvis jeg havde fridag på mandag, ville jeg spise frokost med min mor.

So for learners, it is best to treat this comma as required in sentences like this.

Normally, no. It usually suggests the opposite or at least that the situation is uncertain and hypothetical.

So the feeling is:

If I had Monday off — which I probably don’t — I would eat lunch with my mother.

That is the same nuance as English If I had ... I would ...

If the speaker wanted to sound more neutral or more realistic, they might say something like:

Hvis jeg har fri på mandag, spiser jeg frokost med min mor.

That would sound more like a real possibility.

A more real or open condition would usually use the present tense:

Hvis jeg har fri på mandag, spiser jeg frokost med min mor.

That means:

If I have Monday off, I’ll eat lunch with my mother.

Compare the two:

• Hvis jeg havde fridag på mandag, ville jeg spise frokost med min mor.
  hypothetical / unreal
• Hvis jeg har fri på mandag, spiser jeg frokost med min mor.
  real possibility / open condition

This contrast is very useful in Danish, and it works much like English.