Learn Hardcore Croatian: Na kraju sata ću zapisati datum ispita u bilježnicu. - At the end of the lesson I will write down the date of the exam in the notebook.

na kraju – na
- locative (kraju)
  - With time expressions and static location, na takes the locative:
  - na kraju = at the end (no movement, just a point in time).
kraj then takes genitive to show “end of something”:
- kraj (čega?) sata → sata is genitive singular of sat.

So:

na kraju sata = at the end of the lesson / class
na kraj sata would use accusative (kraj) and would suggest movement to the end, not a time point. It’s not how you say “at the end (of the lesson)”.
na kraju sat is simply ungrammatical: sat must be in genitive (sata) after kraj.

Does sat here mean “hour” or “lesson / class”? Why is it sata?

Literally, sat means “hour” or “clock”, but in a school context it’s also used for a class period:

sat = an hour of time, or a school period
Na kraju sata = At the end of the class / lesson (not just any hour)

The form sata is genitive singular of sat, required by the noun kraj:

kraj sata = the end of the lesson
kraj filma = the end of the film
kraj dana = the end of the day

So sat is “lesson” by context, and sata is just its genitive form.

Where is the word “I” in this sentence? Why isn’t ja written?

Croatian normally drops subject pronouns because the verb ending already shows the person:

ću zapisati → ću is 1st person singular future → I will (write down)

So the subject “I” is understood from ću:

Full form (emphatic): Ja ću zapisati datum ispita u bilježnicu.
Normal, neutral: Na kraju sata ću zapisati datum ispita u bilježnicu.

You only add ja when you want to emphasize it (e.g. I will write it down, not someone else).

How does the future tense work in ću zapisati?

This is the regular Future I in Croatian:

It uses a short form of htjeti (to want) as an auxiliary
- infinitive:
  - ja ću zapisati – I will write down
  - ti ćeš zapisati – you will write down
  - on/ona će zapisati – he/she will write down
  - mi ćemo zapisati – we will write down
  - vi ćete zapisati – you (pl.) will write down
  - oni će zapisati – they will write down

So ću is the auxiliary showing I, future, and zapisati is the main verb in the infinitive.

What’s the difference between ću zapisati and zapisat ću?

Both are correct future forms with the same basic meaning:

ću zapisati datum
zapisat ću datum

The difference is word order and form:

Clitic position: ću is a clitic (short unstressed word) and tends to stand in second position in the clause. That’s why you see:
- Na kraju sata ću zapisati… (ću comes early)
Short infinitive: in zapisat ću, the infinitive zapisati drops the final -i:
- zapisati → zapisat
  - ću

In modern Croatian, both patterns are common:

Na kraju sata ću zapisati datum ispita u bilježnicu.
Na kraju sata zapisat ću datum ispita u bilježnicu.

The meaning is the same; the second version (“short infinitive”) is perhaps a bit more colloquial in feel, but fully standard.

Why is the verb zapisati used and not pisati or zapisivati?

Croatian verbs have aspect: perfective (completed action) vs imperfective (ongoing / repeated).

pisati – imperfective: to write (in general)
zapisivati – imperfective: to be writing down / to write down repeatedly
zapisati – perfective: to write down once, to complete the act of writing it down

In this sentence, the idea is a single, completed action in the future:

I will (once, at that moment) write the exam date down in the notebook.

That’s why zapisati (perfective) is chosen, not pisati or zapisivati.

What cases are in datum ispita, and what does ispita mean here?

datum is in nominative singular (it’s the direct object of zapisati, but Croatian often uses the bare nominative form as the dictionary form; in context it functions as what’s being written).
ispita is genitive singular of ispit (exam), so:
- datum (čega?) ispita → the date of the exam.

So datum ispita literally means “date of exam”.

Also note: Croatian has no articles (the / a), so datum ispita can mean “the date of the exam” in English; “the” is simply understood from context.

Why is it u bilježnicu and not u bilježnici?

The preposition u takes different cases depending on meaning:

u
- accusative → movement into / direction
  - u bilježnicu – into the notebook (you’re putting something there)
u
- locative → location / being in
  - u bilježnici – in the notebook (already inside, static location)

Here the idea is writing something into the notebook, so accusative is used:

zapisati datum u bilježnicu – to write the date into the notebook

If you said datum je u bilježnici, that would mean the date is in the notebook (already written there), using locative.

Is bilježnica the only way to say “notebook”? Any regional notes?

Bilježnica is the standard Croatian word for a school notebook / exercise book.

There are regional variants in other ex-Yugoslav countries:

teka – used in some parts of Croatia and Bosnia (more regional/colloquial)
sveska – common in Serbian and some Bosnian / Montenegrin varieties

In standard Croatian as taught in Croatia, bilježnica is the neutral, textbook choice, and u bilježnicu is exactly how you’d normally say “into (my) notebook”.