Learn Hardcore Croatian: Umoran sam, zato ostajem kod kuće.

Both are correct. Croatian usually drops the subject pronoun, so Umoran sam is the neutral, natural way to say it. Fronting the adjective (Umoran) puts light emphasis on “tired.” Ja sam umoran is fine too, and it emphasizes “I” a bit more (as opposed to someone else).

How does the sentence change if the speaker is female or if it’s plural?

Adjectives agree with the subject.

Female speaker: Umorna sam, zato ostajem kod kuće.
We (mixed or all-male): Umorni smo, zato ostajemo kod kuće.
We (all-female): Umorne smo, zato ostajemo kod kuće.

What exactly does zato do here?

Zato means “therefore/so/that’s why.” It links the first clause (reason) to the second (result). It’s natural to put a comma before it because you’re joining two independent clauses.

What’s the difference between zato and zato što/jer?

zato = “therefore/so” (introduces the result): …, zato ostajem…
jer / zato što = “because” (introduce the reason): Ostajem … jer/zato što sam umoran/umorna. Avoid the redundant mix zato jer in standard language.

Can I start a new sentence with Zato?

Yes. For example: Umoran sam. Zato ostajem kod kuće. This is common and clear.

Why is it kod kuće and not u kući?

kod kuće = “at home” (state, where you are).
u kući = “in the house” (inside the building, literal location).
If you mean the general idea of being at home, use kod kuće.

What case is kuće and why?

Kuće is genitive singular. The preposition kod (“at, by”) requires the genitive: kod + genitive → kod kuće.

When do I use kući, kuću, kuće?

kod kuće (genitive with kod) = at home.
u kući (locative with u) = in the house.
u kuću (accusative with u) = into the house (motion).
kući (dative) = to home/house, mainly with motion: Idem kući = I’m going home.

Is ostajem the right aspect/tense here?

Yes. Ostajem is present of the imperfective verb ostajati and fits an immediate decision or ongoing action (“I’m staying”). For a clear future decision, use perfective ostati: Ostat ću kod kuće (“I will stay at home”).

How do you conjugate ostajati in the present?

ja ostajem
ti ostaješ
on/ona/ono ostaje
mi ostajemo
vi ostajete
oni/one/ona ostaju

Where does the clitic sam go? Can the sentence start with sam?

Clitics like sam tend to the “second position” in a clause. They usually follow the first stressed word or phrase:

Umoran sam / Ja sam umoran are fine.
Starting with Sam umoran is not standard in a full sentence.

Is the comma before zato required?

Yes, you normally place a comma before zato when it connects two independent clauses. Alternatively, split into two sentences: “… Zato …”

Can I use something else instead of zato, like pa, zbog toga, or stoga?

pa = “so/and so” (colloquial): Umoran sam, pa ostajem…
zbog toga = “because of that/for that reason” (neutral): …, zbog toga ostajem…
stoga = “therefore” (more formal): …, stoga ostajem…

What’s the difference between umoran, pospan, iscrpljen, premoren?

umoran = tired.
pospan = sleepy/drowsy.
iscrpljen = exhausted.
premoren = overtired/very tired.

What’s the difference between zato and za to?

zato (one word) = therefore/that’s why.
za to (two words) = for that (preposition + pronoun).
Example: Nemam vremena za to. vs. Zato ostajem kod kuće.

How do I pronounce ć in kuće?

Ć is a softer “ch,” somewhat between English “t” and “ch” (like a soft “tchy”). Don’t confuse it with č, which is a harder “ch” (as in “chocolate”). It’s spelled kuće with ć.

Is doma acceptable instead of kod kuće?

Yes. In Croatian, doma is common and neutral in everyday speech: Ostajem doma. Kod kuće is also perfectly standard.

How do I negate this sentence?

Use the negative of “to be” and of the main verb if needed:

Nisam umoran/umorna, zato ne ostajem kod kuće.
If only the result is negated: Umoran/Umorna sam, ali ne ostajem kod kuće.

Could I drop sam and just say Umoran, zato ostajem…?

In a full sentence, you should keep sam. You can drop it only in very short elliptical answers (e.g., “Kako si?” — “Umoran/Umorna.”), but not in normal declarative sentences.