Il est bien tard, alors je vais me coucher.

In Il est bien tard, il is a dummy subject. It does not refer to a person or thing.

French often requires a subject pronoun even when English would just say It is late with a non-specific it. This is the same kind of it as in:

• Il est minuit. = It is midnight.
• Il est temps de partir. = It is time to leave.

So here, il does not mean he. It just fills the subject position.

Here, bien does not mean well. It is being used as an intensifier.

So Il est bien tard means something like:

• It’s quite late
• It’s really late
• It’s pretty late

This use of bien is very common in spoken and written French. It adds emphasis.

Compare:

• Il est tard. = It’s late.
• Il est bien tard. = It’s really / quite late.

Tard here is used in an impersonal time expression: Il est tard = It is late.

In this expression, tard behaves like a fixed predicate about the time, not like a normal adjective describing a noun. That is why you do not change it for gender or number here.

This is just the standard French way to say it’s late.

Here, alors means so, therefore, or in that case.

In this sentence, it links the two ideas:

• Il est bien tard = It’s quite late
• alors je vais me coucher = so I’m going to bed

Depending on context, alors can also mean then, but here the logical meaning is clearly so / therefore.

Je vais me coucher uses the near future: aller + infinitive.

It literally looks like I am going to go to bed, but in real French it often just means:

• I’m going to bed
• I’m going to go to bed

It is very natural when talking about something you are about to do soon.

Je me coucherai is the simple future, meaning I will go to bed. It is also correct, but it can sound a bit more detached, formal, or simply less immediate.

So in everyday speech, je vais me coucher is very common and natural.

Se coucher is a reflexive verb meaning:

• to go to bed
• to lie down

In many contexts, especially with time expressions like this one, it means to go to bed.

Examples:

• Je vais me coucher. = I’m going to bed.
• Les enfants se couchent à neuf heures. = The children go to bed at nine.

It is related to coucher, which can mean to lay down or to put to bed, but se coucher specifically means that the subject is doing it to themself.

Because se coucher is a reflexive verb.

The reflexive pronoun changes to match the subject:

• je me couche
• tu te couches
• il/elle se couche
• nous nous couchons
• vous vous couchez
• ils/elles se couchent

So me shows that I am the one going to bed.

In English, we usually do not say I put myself to bed in this situation, but French uses the reflexive structure naturally here.

In a construction with aller + infinitive, the reflexive pronoun usually goes in front of the infinitive, not in front of aller.

So:

• je vais me coucher
• tu vas te reposer
• elle va se préparer

That is the normal pattern.

If the verb were not in an infinitive construction, the reflexive pronoun would go before the conjugated verb:

• je me couche = I go to bed
• elle se prépare = she gets ready

Yes, you could say je vais aller au lit, and it would be understood.

But je vais me coucher is usually the more natural and idiomatic choice for I’m going to bed.

There is a slight difference in feel:

• aller au lit = to go to bed / go to the bed
• se coucher = to go to bed / lie down

In many situations they overlap, but se coucher is especially common when talking about going to bed as an action or routine.

Both can mean that it is very late, but they do not feel exactly the same.

• très tard = very late
• bien tard = really / quite / pretty late, often with a slightly more expressive or conversational tone

So:

• Il est très tard sounds straightforward and neutral.
• Il est bien tard sounds a bit more emphatic or expressive.

Both are correct, but bien gives the sentence a little more feeling.

Yes. It sounds perfectly natural.

• Il est tard is a very common expression.
• Il est bien tard adds emphasis in a natural way.
• Alors je vais me coucher also sounds normal and conversational.

A native speaker might say this exactly as written, especially in speech or informal writing.

Yes, depending on context.

The verb se coucher literally refers to lying down or going to bed, so it does not always guarantee that the person intends to sleep immediately.

However, in a sentence like Il est bien tard, alors je vais me coucher, the most natural interpretation is I’m going to bed because it is late.

So context usually makes the meaning clear.