Hyran är en stor utgift.

Because -n is the definite article added to the noun.

• hyra = rent
• hyran = the rent

In Swedish, the definite article is usually attached to the end of the noun instead of being a separate word like English the.

So:

• en hyra = a rent / rent
• hyran = the rent

Here, hyran is the subject of the sentence: the rent.

Because utgift is being used in the indefinite singular here: a big expense.

• en utgift = an expense
• en stor utgift = a big expense
• den stora utgiften = the big expense

Swedish often works like this:

• indefinite noun + adjective: en stor utgift
• definite noun + adjective: den stora utgiften

So in your sentence, hyran is definite (the rent), but en stor utgift is indefinite (a big expense).

Because utgift is an en-word and it is singular indefinite.

Adjectives in Swedish change form depending on the noun:

• en-word singular: stor
• ett-word singular: stort
• plural or definite form: stora

Examples:

• en stor utgift = a big expense
• ett stort problem = a big problem
• stora utgifter = big expenses
• den stora utgiften = the big expense

Since utgift is an en-word, the correct form is stor.

Är is the present tense of vara, which means to be.

So:

• vara = to be
• är = is / are / am depending on context

Examples:

• Jag är trött. = I am tired.
• Hon är här. = She is here.
• Hyran är hög. = The rent is high.

In Swedish, the same form är is used with all subjects in the present tense.

Because this is a normal Swedish main clause with the standard word order:

subject + verb + complement

So:

• Hyran = subject
• är = verb
• en stor utgift = complement

This is very similar to English:

• The rent
  • is
    • a big expense

Swedish main clauses usually put the finite verb in the second position, and here that happens naturally because the subject comes first.

It is an en-word.

You can tell from the phrase:

• en utgift
• en stor utgift

This matters because it affects:

1. the article
   
   • en utgift
2. adjective form
   
   • stor, not stort
3. definite form
   
   • utgiften = the expense

Yes. Hyra can be both a noun and a verb, so context matters.

As a noun:

• en hyra = rent
• hyran = the rent

As a verb:

• att hyra = to rent / to hire

Examples:

• Hyran är hög. = The rent is high.
• Vi vill hyra en bil. = We want to rent a car.

In your sentence, hyran is clearly the noun form.

Är is usually pronounced roughly like air, but shorter and more relaxed, depending on accent.

A few tips:

• ä sounds somewhat like the vowel in English air or bed, depending on dialect
• r is pronounced in the Swedish way, which varies by region

For many learners, a good approximation is:

• är ≈ air

Also, in natural speech, är is often said quite quickly.

Because Swedish usually puts the definite article at the end of the noun.

So instead of:

• English: the rent

Swedish says:

• hyran

This ending carries the meaning of the.

Compare:

• bok = book

• boken = the book

• hyra = rent
• hyran = the rent

Yes. Hyran är stor is grammatical, but it means something slightly different in nuance.

• Hyran är stor = The rent is big/high/large
• Hyran är en stor utgift = The rent is a big expense

The first sentence describes the rent directly.
The second describes what kind of thing it is: a big expense.

So your original sentence is a bit more specific.

The definite singular form is utgiften.

Here are the main forms:

• en utgift = an expense
• utgiften = the expense
• utgifter = expenses
• utgifterna = the expenses

So if you wanted to say the big expense, you would say:

• den stora utgiften

Yes, it sounds natural. Swedish often uses combinations like:

• en stor utgift = a big expense
• en stor kostnad = a big cost
• en hög hyra = a high rent

All of these are natural, though they focus slightly differently:

• stor utgift emphasizes that it is a major expense
• hög hyra emphasizes that the rent itself is high

So Hyran är en stor utgift is a normal and idiomatic sentence.

Almost:

• Hyran = the rent
• är = is
• en stor utgift = a big expense

So the word-for-word translation is:

The rent is a big expense.

That works well in English too, so this sentence matches English structure quite closely.