Mój samochód jest w domu.

to be

Breakdown of Mój samochód jest w domu.

• mój: my
• w: at
• samochód: car

Questions & Answers about Mój samochód jest w domu.

Why is it mój samochód and not moja or moje?

Because the possessive pronoun must agree with the noun it describes in gender, number, and case.
Samochód is masculine singular in the nominative (it’s the subject), so you use mój.
Other forms:

• moja = feminine singular (e.g., moja książka)
• moje = neuter singular or plural non-masculine-personal (e.g., moje dziecko, moje auta)
• moi = masculine personal plural (e.g., moi koledzy)

What case is samochód in here?

Samochód is in the nominative case because it’s the subject of the sentence (the thing being talked about: my car).

Is jest required, or can I leave it out?

In the present tense, Polish often omits the verb jest (to be), especially in simple statements. Both are common:

• Mój samochód jest w domu. (explicit, neutral)
• Mój samochód w domu. (more conversational/elliptical)

Including jest can sound a bit more complete or emphatic, depending on context.