Learn Hardcore Czech: Moje sestra je doma v novém bytě. - My sister is at home in a new apartment.

Because sestra (sister) is a feminine noun, and Czech possessive pronouns must agree in gender, number, and case with the noun they modify.

můj – masculine singular (e.g., můj bratr – my brother)
moje – feminine singular (e.g., moje sestra – my sister)

So moje sestra is the correct combination.
If the noun were neuter (e.g., dítě – child), you’d also use moje: moje dítě (my child).

Can I also say Má sestra instead of Moje sestra? What’s the difference?

Yes, both are grammatically correct:

Moje sestra – the most common, neutral, everyday form.
Má sestra – a shorter, more formal or literary variant.

You’ll see má / mé / můj forms more often in written texts, literature, or slightly elevated style.
In casual spoken Czech, moje sestra is more natural.

Why is sestra in this form and not something like sestru?

In this sentence, sestra is the subject (“who” is at home?), so it appears in the nominative case.

Nominative singular of sestra is sestra.
Forms like sestru are other cases (e.g., accusative: Vidím sestru. – I see my sister).

Here we are simply stating: My sister (subject) is at home, so nominative sestra is required.

What exactly is doma? Is it a noun like “home”, or something else?

Doma is an adverb, not a noun. It means “at home” (state, location).

Contrast:

dům – a house (noun)
domov – home in a more abstract sense, “home” as a place you belong
doma – at home (adverb, describes where someone is)
domů – (to) home (direction, “homeward”)

Examples:

Jsem doma. – I am at home.
Jdu domů. – I’m going home.
Můj domov je tady. – My home is here.
Ten dům je velký. – That house is big.

In your sentence, doma simply tells us where she is: at home.

Why do we have both doma and v novém bytě? Doesn’t doma already mean “at home”?

Yes, doma means “at home”, but v novém bytě adds extra specific information about where “home” is.

Moje sestra je doma. – My sister is at home. (no further detail)
Moje sestra je doma v novém bytě. – My sister is at home in the new apartment. (home = that particular apartment)

So doma gives the general idea of being at home, and v novém bytě specifies which place is her home in this context.

Could the word order be Moje sestra je v novém bytě doma? Does that change the meaning?

Yes, Moje sestra je v novém bytě doma is also grammatically correct.

The basic meaning remains the same, but the focus shifts slightly:

Moje sestra je doma v novém bytě.
- feels like “My sister is at home in the new apartment”
  (mild focus on doma first, then specifying where that is)
Moje sestra je v novém bytě doma.
- can emphasize that in that new apartment, she feels at home or that that’s where she is at home.

Word order in Czech is relatively flexible, but it affects emphasis and rhythm, not basic grammar. For a neutral statement, your original word order is perfectly natural.

What case is v novém bytě and why is that case used?

V novém bytě uses the locative case:

novém – locative masculine singular of nový
bytě – locative masculine singular of byt

In Czech, the preposition v:

with location (“in, inside”) uses the locative case:
- v bytě – in the apartment
- v autě – in the car
- ve škole – at school / in school
with movement into (“into”) you’d use v + accusative only in some fixed expressions, but usually Czech uses do + genitive for “into”:
- jdu do bytu – I’m going into the apartment (genitive bytu)

In your sentence, she is in the apartment (location, not movement), so v + locative → v novém bytě.

Why is the adjective novém in that particular form?

Novém is in the locative masculine singular form, because it has to agree with the noun bytě:

byt – masculine, inanimate
locative singular of byt is bytě
corresponding form of nový (new) in masculine inanimate locative singular is novém

So:

nominative: nový byt – a new apartment
locative: v novém bytě – in the new apartment

Adjectives in Czech always match the noun’s gender, number, and case.

Why does byt change to bytě with an ě at the end?

This is just the regular declension pattern for many masculine inanimate nouns ending in a consonant.

For byt (apartment):

Nominative singular (dictionary form): byt
Locative singular: bytě

The -ě ending marks the locative case here.
Other examples:

hrad (castle) → v hradě
les (forest) → v lese
svět (world) → ve světě

So byt → bytě follows the standard pattern “-t” + “-ě” in the locative.

Can I say Moje sestra je v novém bytě without doma? How does that differ?

Yes:

Moje sestra je v novém bytě.
– My sister is in the new apartment.

This simply states her location.

Moje sestra je doma v novém bytě.
– My sister is at home in the new apartment.

Including doma can add a nuance that this is her home, not just a place she happens to be (like visiting a friend’s flat). Without doma, you’re not explicitly saying it’s her home, just that she is physically there.

Is the verb je (is) necessary here, or can it be omitted like in some Slavic languages?

In standard Czech, in normal sentences like this, you do use the verb je:

Moje sestra je doma v novém bytě. – correct, natural.

Omitting je is:

common in headlines, slogans, poetry, or very stylized texts:
- Praha krásná (headline style) – Prague (is) beautiful.
possible in some set expressions (e.g., Všechno v pořádku? – everything (is) OK?)

But “Moje sestra doma v novém bytě” without je sounds incomplete or unnatural in normal speech or writing.
So for everyday usage, keep “je”.