Hvis du ikke gider at gå ud i regnen, bliver jeg også hjemme.

In this sentence, gide means something like feel like, be willing to, or can be bothered to.

So du ikke gider at gå ud i regnen means:

• you don’t feel like going out in the rain
• you can’t be bothered to go out in the rain

It is a very common everyday Danish word, and in the negative it often sounds casual and natural.

Because Hvis du ikke gider at gå ud i regnen is a subordinate clause introduced by hvis.

In Danish subordinate clauses, words like ikke usually come before the finite verb.

Compare:

• Du gider ikke gå ud i regnen.
  main clause

• Hvis du ikke gider at gå ud i regnen ...
  subordinate clause

So this word order is normal and important to learn.

After gide, Danish can use an infinitive with at.

So gider at gå is grammatical and natural.

You will also often hear gider gå without at, especially in everyday speech. So both patterns exist:

• Jeg gider ikke at vente.
• Jeg gider ikke vente.

In your sentence, gider at gå is perfectly fine.

It is built from two parts:

• gå ud = go out / go outside
• i regnen = in the rain

Together, gå ud i regnen means go out into the rain or go outside in the rain.

So the idea is not just walking in general, but specifically going outside when it is raining.

This is because Danish main clauses follow the V2 rule: the finite verb comes in the second position.

The sentence begins with a whole subordinate clause:

• Hvis du ikke gider at gå ud i regnen

After that, the main clause starts. Since the first position is already taken by the if-clause, the finite verb comes next:

• bliver jeg også hjemme

If the main clause stood alone, it would be:

• Jeg bliver også hjemme.

So the inversion is caused by the fronted hvis-clause.

Because blive hjemme means stay home or remain at home.

That is different from være hjemme, which means be at home.

Compare:

• Jeg er hjemme. = I am at home.
• Jeg bliver hjemme. = I am staying home / I will stay home.

In this sentence, the speaker is making a decision not to go out, so bliver hjemme is the right choice.

Because hjemme usually expresses location: at home.

So:

• Jeg er hjemme. = I am at home.
• Jeg bliver hjemme. = I stay home.

By contrast, hjem often expresses direction or movement toward home:

• Jeg går hjem. = I am going home.

That is why bliver hjemme is correct here.

Også means also or too.

Here it shows that the speaker will do the same kind of thing:

• if you stay home,
• I will also stay home.

So jeg også hjemme has the sense of I too will stay home.

Without også, the sentence would simply mean I’ll stay home, but it would lose the idea of too/as well.

Its position is normal for Danish sentence structure.

If the clause stood alone, you would usually say:

• Jeg bliver også hjemme.

After the initial hvis-clause, the verb and subject switch:

• bliver jeg også hjemme

So også stays in its usual place inside the clause, after the finite verb-subject sequence.

Danish often uses the present tense for future meaning when the context is clear.

That is what happens here:

• Hvis du ikke gider ...
• bliver jeg også hjemme.

Even though it refers to what will happen, present tense sounds natural in Danish.

English often uses will in the main clause, but Danish very often does not need a special future form.

Yes, but the meaning changes a little.

• ikke gider = don’t feel like / can’t be bothered to
• ikke vil = don’t want to / refuse to / won’t

So:

• Hvis du ikke gider at gå ud i regnen ...
  sounds casual and natural

• Hvis du ikke vil gå ud i regnen ...
  sounds more direct and more clearly about unwillingness

In many situations, ikke gider is softer and more conversational.

Because the first part is a subordinate clause and the second part is the main clause.

Danish normally separates them with a comma here:

• Hvis du ikke gider at gå ud i regnen, bliver jeg også hjemme.

So the comma marks the boundary between the if-clause and the result clause.