Nedostaje mi novac.

Because mi is the dative form of ja.

With nedostajati, Serbian usually uses this pattern:

• something
  • nedostaje
    • someone in the dative

So in Nedostaje mi novac, the idea is structurally closer to:

• Money is lacking to me

That is why Serbian uses mi rather than ja.

Some dative forms of personal pronouns are:

• mi = to me
• ti = to you
• mu / joj = to him / to her
• nam / vam / im = to us / to you (plural/formal) / to them

Because the verb agrees with novac, not with mi.

In this sentence, novac is the grammatical subject, and novac is singular. So the verb must also be singular:

• novac nedostaje

The word mi is just the indirect object in the dative case, so it does not control the verb form.

Compare:

• Nedostaje mi novac. = singular subject
• Nedostaju mi pare. = plural subject

In the second sentence, pare is plural, so the verb becomes nedostaju.

Novac is in the nominative singular.

That may feel strange to an English speaker, because in English the person often feels like the subject: I am missing money or I lack money. But in Serbian, with nedostajati, the thing that is missing is usually the grammatical subject.

So:

• novac = nominative subject
• mi = dative experiencer/receiver

A very literal breakdown is:

• Nedostaje = is lacking / is missing
• mi = to me
• novac = money

So the structure is basically:

• Money is lacking to me

This is one of those places where Serbian grammar organizes the sentence differently from natural English.

Very often, yes.

A common pattern is:

• X nedostaje Y-u
• Something is missing/lacking to someone

Examples:

• Nedostaje mi vreme. = Time is lacking to me.
• Nedostaje joj hrabrost. = Courage is lacking to her.
• Nedostaju nam informacije. = Information is lacking to us.

It is also used for missing a person or thing emotionally:

• Nedostaješ mi. = I miss you.
• Nedostaje mi Beograd. = I miss Belgrade.

So the same verb can mean both to be lacking and to be missed, depending on context.

Because Serbian usually expresses this idea from the perspective of the missing thing, not the person.

English often says:

• I miss you
• I lack money

Serbian often says:

• You are missing to me → Nedostaješ mi
• Money is lacking to me → Nedostaje mi novac

So it is best to learn nedostajati as a verb that commonly takes:

• the thing/person missing as subject
• the person affected in the dative

Yes. Serbian word order is flexible, though the neutral version here is:

• Nedostaje mi novac.

Other possible orders include:

• Novac mi nedostaje.
• Mi nedostaje novac. (possible, but less neutral and more marked)
• Novac nedostaje meni. (emphatic, with *meni instead of clitic mi)*

The most natural everyday version is usually Nedostaje mi novac.

Serbian often puts short pronouns like mi in an early position in the sentence, which is why Nedostaje mi novac sounds so normal.

Both are dative forms meaning to me, but they are used differently:

• mi = unstressed clitic form
• meni = stressed/full form

So:

• Nedostaje mi novac. = normal, neutral
• Meni nedostaje novac. = emphasizes me
• Novac nedostaje meni, a ne njemu. = The money is lacking to me, not to him.

In most ordinary statements, mi is the one you want.

They are similar in meaning, but not identical in nuance.

• Nedostaje mi novac.
  = I am short of money / I lack money.
  This emphasizes that money is insufficient or missing.

• Treba mi novac.
  = I need money.
  This emphasizes need, not necessarily current shortage.

• Nemam novca.
  = I don’t have money / I have no money.
  This simply states absence.

So these are related, but not interchangeable in every situation.

Yes, and it is very common in everyday speech.

• novac = money, a bit more neutral/formal/general
• pare = money, very common in conversation

Because pare is plural in form, the verb changes too:

• Nedostaje mi novac.
• Nedostaju mi pare.

Both are natural, but pare often sounds more colloquial.

The infinitive is nedostajati.

This is the imperfective verb, which is the normal choice in a sentence like this:

• Nedostaje mi novac.

There is also a perfective partner, usually nedostati, used for completed events or future-like single occurrences in the right context.

Very roughly:

• nedostajati = to be lacking / to be missing (ongoing, repeated, general)
• nedostati = to come to be lacking / to fail to be enough (completed event)

For learners, the most important form to master first is the imperfective nedostajati, because it is the one you will most often use in everyday sentences like this.

Here are the present-tense forms:

• ja nedostajem
• ti nedostaješ
• on/ona/ono nedostaje
• mi nedostajemo
• vi nedostajete
• oni/one/ona nedostaju

But remember: in sentences like Nedostaje mi novac, the verb agrees with the thing/person being missed or lacking, not with the person in dative.

That is why:

• Nedostaje mi novac.
• Nedostaješ mi ti.
• Nedostaju mi prijatelji.