Learn Hardcore German: Bevor ich endgültig einschlafe, denke ich daran, wie viel ich heute gelernt habe. - Before I finally fall asleep, I think about how much I learned today.

Bevor ich endgültig einschlafe – introduced by the subordinating conjunction bevor (before).
… wie viel ich heute gelernt habe – introduced by wie viel as an indirect question.

In German, in subordinate clauses the conjugated verb moves to the final position:

Main clause: Ich schlafe endgültig ein.
Subordinate: … bevor ich endgültig einschlafe.
Direct question: Wie viel habe ich heute gelernt?
Indirect question: Ich frage mich, wie viel ich heute gelernt habe.

So the word order in the sentence is completely normal for German subordinate clauses.

What is the difference between schlafen and einschlafen, and why is it einschlafe here?

schlafen = to sleep (the state)
- Ich schlafe. – I am sleeping.
einschlafen = to fall asleep (the process of going to sleep)
- Ich schlafe ein. – I am falling asleep.

In a main clause, the separable prefix ein- goes to the end:

Ich schlafe ein.

In a subordinate clause, the verb appears as one word at the end:

… bevor ich endgültig einschlafe.

So einschlafe is just schlafe + ein “reunited” at the end of the subordinate clause.

What does endgültig add here? Could I just say Bevor ich einschlafe?

You can say Bevor ich einschlafe, and it’s grammatically fine.
Endgültig adds nuance:

endgültig ≈ for good, once and for all, completely, finally in the sense of not waking up again soon / not just dozing.

So:

Bevor ich einschlafe – before I fall asleep (neutral).
Bevor ich endgültig einschlafe – before I finally / properly fall asleep (e.g. after tossing and turning, or after several short naps).

It emphasizes the final transition into full sleep.

Is endgültig the same as endlich?

No, they are related in meaning but used differently:

endlich = finally, at last
- Focus on the speaker’s feeling that something took a long time.
- Endlich schlafe ich ein. – At last I’m falling asleep.
endgültig = final, definitive, once and for all
- Focus on the fact that something is final / conclusive.
- Ich bin endgültig eingeschlafen. – I fell asleep for good / properly.

In this sentence endgültig is correct; endlich einschlafen would mean “to finally manage to fall asleep (after a struggle)”, which is a slightly different nuance.

Why is there a comma before denke: „…, denke ich daran, …“?

The comma marks the end of the subordinate clause started by Bevor:

Bevor ich endgültig einschlafe, ← subordinate clause
denke ich daran, … ← main clause

In German, subordinate clauses are always separated by a comma from the main clause. Here, the subordinate clause comes first, so it is followed by a comma before the main clause begins.

What exactly does daran mean in „denke ich daran“, and why is it needed?

The verb denken often takes the preposition an:

an etwas denken – to think of / about something

Example:

Ich denke an meinen Tag. – I think about my day.

When the “something” is another clause (a whole idea like “how much I learned”), German often uses a da(r)-compound:

Ich denke daran, wie viel ich heute gelernt habe.
Literally: I think of that, how much I learned today.
Natural English: I think about how much I learned today.

So daran = da- + an and functions as a placeholder object for the following clause. It’s required by the verb denken an to link the verb to the clause.

Can I leave out daran and just say: „denke ich, wie viel ich heute gelernt habe“?

No, that would sound wrong in German.

denken by itself does not directly take a wie / dass / ob-clause as its object the way English “think (that) …” can.
You either need:
- denken, dass … (think that …)
- or an etwas denken / daran denken (think about something / think of it).

Here, English has “I think about how much I learned …”, so the natural German pattern is an etwas denken → daran denken, followed by the clause:

Ich denke daran, wie viel ich heute gelernt habe.

Without daran, the sentence feels incomplete/ungrammatical.

What is the function of wie viel here? Why not wieviel?

Wie viel functions as the start of an indirect question:

Direct: Wie viel habe ich heute gelernt? – How much did I learn today?
Indirect: Ich denke daran, wie viel ich heute gelernt habe. – I think about how much I learned today.

Spelling:

Traditional rule: wie viel is usually written as two words, especially when it literally means “how much” in a question or indirect question.
wieviel as one word is sometimes seen, but wie viel is the preferred and more standard modern spelling in this context.

So here wie viel is correct and standard.

Why is it „wie viel ich heute gelernt habe“ and not „wie viel habe ich heute gelernt“?

„Wie viel habe ich heute gelernt?“ is a direct question:

Verb in second position: habe
Final question mark
Spoken with questioning intonation.

In the sentence given, this is an indirect question embedded inside another statement:

Ich denke daran, wie viel ich heute gelernt habe.
– I think about how much I learned today.

In indirect questions, German uses subordinate clause word order:

The finite verb goes to the end: gelernt habe
No question mark for this clause (the main sentence decides the punctuation).

So:

Direct: Wie viel habe ich heute gelernt?
Indirect: … wie viel ich heute gelernt habe.

Why is the perfect tense split as „gelernt habe“ instead of „habe gelernt“?

In German, the present perfect is made of:

Auxiliary: haben or sein
Past participle: gelernt, geschlafen, gegangen, etc.

Word order depends on the type of clause:

Main clause: auxiliary in 2nd position, participle at the end
- Ich habe heute viel gelernt.
Subordinate clause: both elements go to the end, in the order
participle + auxiliary
- … weil ich heute viel gelernt habe.

In „wie viel ich heute gelernt habe“, this is a subordinate clause (indirect question), so you get:

gelernt (participle) + habe (auxiliary) at the end of the clause.

That’s why it’s gelernt habe here.

Why is the present perfect (habe gelernt) used here instead of a simple past form?

In spoken and informal written German, the present perfect (Perfekt) is more common than the simple past (Präteritum) for most verbs when talking about completed actions in the past, especially in everyday contexts:

Ich habe heute viel gelernt. (normal, everyday)
Ich lernte heute viel. (correct, but sounds written/literary or a bit old-fashioned in many regions)

The sentence describes what was learned earlier today, something that is finished but still relevant now as the speaker is falling asleep. The Perfekt fits that situation very well.

So „wie viel ich heute gelernt habe“ is the natural, conversational choice.

Why is heute in the middle: „wie viel ich heute gelernt habe“ and not at the start or end?

In German, time adverbs like heute are quite flexible, but the position used here is very typical:

Subject → ich
Time → heute
Object/other elements → (here none between)
Verb part 1 → gelernt
Auxiliary → habe

So: … wie viel ich heute gelernt habe.

Other positions are possible:

… wie viel ich gelernt habe heute. (possible, but less neutral; often adds emphasis or sounds more spoken/colloquial)
… wie viel ich heute gelernt habe. (most neutral/natural here)

Placing heute after the subject and before the main verb is the standard neutral position for time in many sentences.