Ako dugo ostanem u minusu, banka će mi opet povećati kamatu.

After ako for a real future condition, Croatian normally uses the present tense, not the future tense.

So:

• Ako dugo ostanem u minusu... = If I stay / if I remain in overdraft for a long time...
• not Ako ću ostati...

This is actually similar to English, where we say If I stay..., not If I will stay...

Also, ostanem is the 1st person singular present form of ostati.

This is a question of verb aspect.

• ostanem = perfective
• ostajem = imperfective

In this sentence, ostanem is used because the speaker is talking about the result or outcome of the situation: if I remain/end up staying in the red for a long time.

If you used ostajem, it would sound more like an ongoing or habitual situation, not the same kind of future condition.

So Ako dugo ostanem u minusu... is the natural choice here.

U minusu is a very common banking/financial expression meaning:

• in the red
• overdrawn
• with a negative balance
• sometimes more loosely in debt

Literally, it means in minus, but in natural English you would not usually translate it that literally.

Because u here takes the locative case when it means being in a place or state.

• base form: minus
• locative singular: minusu

So:

• u minusu = in overdraft / in the red

This is the same general idea as:

• u banci = in the bank
• u gradu = in the city

Here it is not a physical place, but a financial state.

Dugo means for a long time or long in the sense of duration.

It is an adverb, and it modifies ostanem:

• dugo ostanem = stay/remain for a long time

So the sentence is not just about being overdrawn, but about being overdrawn for a long enough period that the bank reacts.

Mi is the short dative form of ja.

Here it means something like:

• to me
• for me
• in natural English, often simply my

So:

• banka će mi povećati kamatu

literally = the bank will increase the interest to me

but natural English is:

• the bank will raise my interest rate

Croatian often uses the dative pronoun where English prefers a possessive structure.

Because kamatu is the accusative singular of kamata.

• dictionary form: kamata
• accusative singular: kamatu

It is accusative because it is the direct object of povećati:

• povećati što? → kamatu

So:

• banka će povećati kamatu = the bank will increase the interest / interest rate

In banking, kamata can refer to interest in general, but in a sentence like povećati kamatu, English often translates it more naturally as raise the interest rate.

So depending on context, you may see:

• increase the interest
• raise the interest rate

In this sentence, interest rate is usually the most natural English interpretation.

Because će is a clitic. Croatian clitics usually go in the second position of the clause.

In the main clause:

• banka is the first stressed word
• so će comes right after it

That gives:

• banka će mi opet povećati kamatu

The pronoun mi is also a clitic, so it joins the clitic group near the beginning of the clause.

This word order is very normal and natural in Croatian.

Opet means again.

Here it shows that this is not the first time the bank has done this:

• banka će mi opet povećati kamatu = the bank will raise my interest rate again

Its position is somewhat flexible. For example, Croatian may also allow slightly different placements depending on emphasis. But in this sentence, the chosen position is completely natural.

Because Croatian often drops subject pronouns when the verb ending already shows who the subject is.

• ostanem already tells you the subject is I
• so ja is unnecessary unless you want emphasis

Compare:

• Ako dugo ostanem u minusu... = neutral
• Ako ja dugo ostanem u minusu... = more emphatic, maybe contrasting me with someone else

This is one of the big differences from English, where the subject pronoun usually has to be stated.

Yes. In standard Croatian, the ako clause and the main clause are separated by a comma.

So:

• Ako dugo ostanem u minusu, banka će mi opet povećati kamatu.

The comma marks the boundary between the conditional clause and the main clause.

This is true whether the ako clause comes first or after the main clause in standard writing.