Я дома, поскольку сегодня выходной.

In Russian, the verb to be is normally omitted in the present tense.

So:

• Я дома = I am at home
• literally, something like I at home

You would not normally say Я есть дома in modern standard Russian.

Compare:

• Я дома = I am at home
• Я был дома = I was at home
• Я буду дома = I will be at home

So the verb appears in the past and future, but not usually in the present.

Because дома means at home, while домой means to home / homeward.

This is a very common distinction:

• Я дома = I am at home
• Я иду домой = I am going home

A useful way to remember it:

• дома = location
• домой = direction/movement

So in this sentence, the speaker is already at home, not moving there.

Дома is the normal idiomatic way to say at home in Russian.

• Я дома = I am at home

If you say в доме, that usually means in the house/building, with more emphasis on the physical building itself rather than the idea of home.

Compare:

• Я дома = I’m at home
• Я в доме = I’m in the house

English often uses home and house differently, and Russian does something similar here.

Поскольку means since or because.

In this sentence:

• Я дома, поскольку сегодня выходной.
• I’m at home, since/because today is a day off.

Compared with other Russian words for because:

• потому что = the most common neutral way to say because
• так как = also since/because, often a bit more formal or written
• поскольку = since/as/because, often slightly more formal or explanatory

So this sentence could also be said as:

• Я дома, потому что сегодня выходной.

That may sound more conversational to many learners.

Because поскольку introduces a subordinate clause.

The sentence has two parts:

• Я дома = main clause
• поскольку сегодня выходной = subordinate clause explaining the reason

In Russian, clauses introduced by conjunctions like потому что, так как, and поскольку are normally separated by a comma.

So the comma here is standard and necessary.

Literally, it means something like:

• today [is] a day off

Again, Russian omits the present-tense is.

So:

• сегодня выходной = today is a day off / today is a day off for me / today is my day off

Depending on context, it can mean:

• today is a non-working day
• today is a holiday
• I have the day off today

Russian often leaves this a bit more implicit than English does.

Here выходной is being used like a noun, but historically it comes from an adjective, as in:

• выходной день = a day off / a non-working day

Very often, день is simply omitted because it is understood:

• Сегодня выходной (день).

Since the hidden noun день is masculine singular, выходной also appears in the masculine singular form.

So you can think of this as an abbreviated version of Сегодня выходной день.

In practical terms, learners can treat it as a noun-like word meaning day off in this sentence.

More technically, it is an adjective used substantively (that is, used as a noun), with the implied noun день understood.

So both of these ideas help:

• full form: выходной день
• shortened normal form: выходной

This kind of shortening is very common in Russian.

Its most direct meaning is I am at home or I’m home.

Depending on context, it can also imply I’m staying home for the day, especially when followed by a reason:

• Я дома, поскольку сегодня выходной.

This can naturally suggest:

• I’m at home because today is a day off
• I’m home today because it’s a day off

So the exact English translation depends on context, but the core idea is simply location/state: at home.

Yes. Выходной is fairly flexible.

It can mean:

• an official non-working day
• a weekend day
• a public holiday
• someone’s personal day off from work

Context tells you which one is meant.

So сегодня выходной can mean:

• today is a day off
• today is a holiday
• I have the day off today

without always specifying exactly what kind of day off it is.

The word order can change, although the original sentence is perfectly natural.

Original:

• Я дома, поскольку сегодня выходной.

Possible alternatives:

• Поскольку сегодня выходной, я дома.
• Я дома, потому что сегодня выходной.
• Сегодня выходной, поэтому я дома.

These all express a similar idea, but with slightly different focus or style.

A rough comparison:

• Я дома, поскольку сегодня выходной. = neutral, somewhat formal
• Поскольку сегодня выходной, я дома. = puts the reason first
• Я дома, потому что сегодня выходной. = very common everyday style
• Сегодня выходной, поэтому я дома. = today is a day off, therefore I’m at home

Here it is pronounced до́ма, with the stress on the first syllable.

That is important because дома can also be the genitive singular form of дом, and then the stress is different:

• до́ма = at home
• дома́ = of the house / at home? No — in standard pronunciation, this form is the genitive singular or related noun form with final stress

For this sentence, the meaning is definitely at home, so the pronunciation is до́ма.

Yes, absolutely.

• Я дома, поскольку сегодня выходной.
• Я дома, потому что сегодня выходной.

Both mean the same thing here.

The difference is mostly style:

• потому что = more common in everyday speech
• поскольку = often a bit more formal, written, or explanatory

So if you are a beginner and want the most natural everyday version, потому что is often the easiest choice.