Learn Hardcore Croatian: Ovaj tjedan na poslu je stresan.

Tjedan is in the nominative singular because it is the subject of the sentence: Ovaj tjedan = this week.
Other forms like tjedna (genitive) or tjednu (dative/locative) are used when the week is not the subject but is governed by a preposition or verb, e.g. tijekom ovog tjedna (during this week), u ovom tjednu (in this week – rarer, more formal).

What case is na poslu, and why is that form used?

Na poslu is locative singular of posao (job, work).
The preposition na + locative is used to express being at a place:

na poslu – at work
na fakultetu – at (the) university
So posao changes to poslu in the locative.

What is the difference between posao and poslu?

They are different cases of the same noun:

posao – nominative singular (dictionary form, subject):
- Moj posao je težak. – My job is hard.
poslu – dative/locative singular (used with some prepositions and for indirect objects):
- Na poslu je stresno. – It is stressful at work.
- Idem na posao. – I’m going to work. (here na posao is accusative)

In your sentence, na poslu is locative: at work.

Why is the adjective stresan and not stresno or stresna?

In Croatian, adjectives agree with the noun in gender, number, and case.

tjedan is masculine singular nominative, so the adjective must also be masculine singular nominative → stresan.

Basic pattern for this adjective in singular:

masculine: stresan tjedan – a stressful week
feminine: stresna godina – a stressful year
neuter: stresno razdoblje – a stressful period

So here stresan is correct because it describes tjedan.

Could the sentence also be Ovaj tjedan je stresan na poslu? Is there any difference?

Yes, Ovaj tjedan je stresan na poslu is grammatically correct.

Both:

Ovaj tjedan na poslu je stresan.
Ovaj tjedan je stresan na poslu.

mean roughly the same. The difference is in emphasis and rhythm, not in basic meaning.
The original version slightly groups na poslu more tightly with ovaj tjedan (this week at work), while the other version may sound a bit more like “this week is stressful at work” with more focus on stresan at the end. In everyday speech, both are fine.

Could I say Ovaj tjedan na poslu je stresno? Would that be more natural?

Yes, Ovaj tjedan na poslu je stresno. is also correct and actually quite common.

The nuance:

Ovaj tjedan na poslu je stresan. – This week at work is stressful (treating “week” as the stressed thing).
Ovaj tjedan na poslu je stresno. – literally This week, at work, it is stressful (impersonal “it is stressful”, focusing more on the general situation at work).

Many speakers might prefer stresno in conversation here because they’re really describing the situation at work, not the “week” as an object.

Why is the verb je in the middle of the sentence and not always right after the subject or at the end?

Je is the 3rd person singular of biti (to be), meaning is. Croatian has flexible word order, so je can move around more than in English.

Possible (and correct) variants include:

Ovaj tjedan na poslu je stresan.
Ovaj tjedan na poslu stresan je.
Stresan je ovaj tjedan na poslu.

The meaning stays the same; you mainly change emphasis and style. The version you have is a very normal, neutral word order.

Can I drop je and just say Ovaj tjedan na poslu stresan?

In standard Croatian, you should not drop je here; the sentence would be considered incomplete or very colloquial/telegraphic.

In informal speech, Croatians sometimes omit present forms of biti (je, sam, si…) in short phrases or headlines, but in a normal sentence like this you are expected to use je:

✅ Ovaj tjedan na poslu je stresan.
❌ Ovaj tjedan na poslu stresan. (sounds like a note or a broken sentence)

What is the difference between ovaj tjedan and ovog tjedna?

ovaj tjedan is nominative → usually used as a subject or in a simple time expression:
- Ovaj tjedan je stresan. – This week is stressful.
- Dolazim ovaj tjedan. – I’m coming this week.
ovog tjedna is genitive → often means during this week / of this week:
- Tijekom ovog tjedna radim puno. – During this week I work a lot.
- Cijelog ovog tjedna sam umoran. – I’ve been tired this whole week.

Both can translate as “this week”, but the case changes according to grammar and often adds a nuance of “during” with the genitive.

Why is the preposition na used with poslu instead of u?

With posao, the typical idiomatic phrase for “at work” is na poslu, not u poslu.

General idea:

na
- locative: on / at a location or activity
- na poslu – at work
- na fakultetu – at university
- na sastanku – at a meeting
u
- locative: in / inside something
- u uredu – in the office
- u zgradi – in the building

So you normally say na poslu to mean “at work” (as a place or situation).

How would the sentence change in the past or future tense?

Present (your sentence):

Ovaj tjedan na poslu je stresan. – This week at work is stressful.

Past:

Ovaj tjedan na poslu je bio stresan. – This week at work was stressful.
(for a specific week that has just ended or in narrative)

Future:

Ovaj tjedan na poslu će biti stresan. – This week at work will be stressful.
Spoken form often contracts će biti to bit će:
Ovaj tjedan na poslu bit će stresan.

How do you pronounce tjedan, especially the tj?

Tjedan is pronounced approximately [tyeh-dahn]:

tj is like a soft “ty” sound, similar to “t”
- “y” in “tune” (British-like pronunciation) or like the “ty” in “atyet”.
je is like “ye” in “yes”.
Stress is typically on the first syllable: TJE-dan.

So: tjedan ≈ TYEH-dahn.