Reći ću ti tačno kada počinje predstava.

Both are possible, but Reći ću is very natural in Serbian.

A few things are happening here:

• ću is a clitic form of hteti used to make the future tense.
• Clitics usually prefer the second position in the sentence or clause.
• When the infinitive comes first, Serbian often splits the future construction:
  • Reći ću
  • instead of Ja ću reći

So:

• Reći ću ti... = a very normal, neutral way to say it
• Ja ću ti reći... = also correct, but ja adds emphasis, like I will tell you...

In other words, the sentence without ja sounds more neutral and natural unless you specifically want contrast or emphasis.

Reći ću is the future tense.

It is made from:

• the infinitive or infinitive stem of the verb
• plus the clitic future forms of hteti: ću, ćeš, će, ćemo, ćete, će

Here the verb is reći = to say / to tell, and:

• reći ću = I will say / I will tell

This is the standard way to form the future in Serbian.

Reći means to say / to tell in the sense of a single completed act: telling someone something.

That fits this sentence well, because the speaker is promising one specific act of telling.

• reći = perfective, one completed statement
• govoriti = to speak / to talk / to be speaking, often more ongoing or repeated
• kazati = also means to say / to tell, but reći is more common in everyday speech

So Reći ću ti... sounds the most natural here.

Ti here means to you.

It is the dative singular form of ti and functions as an indirect object:

• Reći ću ti... = I will tell you...

Why not tebe?

• tebe is an accusative/genitive form, often used for emphasis or after prepositions
• after reći in the sense tell someone something, Serbian uses the dative for the person receiving the information

So:

• reći nekome nešto = to tell someone something
• nekome is dative
• therefore: ti

Tačno means exactly / precisely here.

It tells us that the speaker will give the exact information, not just an approximate answer.

So the idea is:

• not just I’ll tell you when it starts
• but I’ll tell you exactly when it starts

In this sentence, tačno works as an adverb modifying the whole idea of telling the time precisely.

Yes. Kad and kada both mean when.

In everyday Serbian, kad is extremely common and often sounds more conversational:

• Reći ću ti tačno kad počinje predstava.

This is perfectly natural.

Very roughly:

• kada = a bit fuller, sometimes slightly more formal or careful
• kad = more everyday and shorter

Both are correct.

This is very common in Serbian.

After words like kad / kada meaning when, Serbian often uses the present tense to talk about a future event, especially in subordinate clauses.

So:

• kada počinje predstava literally looks like when the performance starts / is starting
• but it naturally refers to a future event in context

English often does something similar:

• I’ll tell you when the show starts not usually
• I’ll tell you when the show will start

So Serbian and English are actually quite similar here.

Because kada itself introduces the subordinate clause.

In English, after verbs like tell, you might sometimes think of structures with that, but here the clause is already introduced by when.

Compare:

• I’ll tell you that the show starts at 8.
• I’ll tell you when the show starts.

In Serbian, the same distinction exists:

• Reći ću ti da predstava počinje u osam. = I’ll tell you that the performance starts at eight.
• Reći ću ti kada počinje predstava. = I’ll tell you when the performance starts.

So da is not needed because kada is already doing the linking.

Predstava is in the nominative singular because it is the subject of počinje.

• predstava = the performance / show
• počinje = starts / begins

So the structure is:

• predstava počinje = the performance starts

Since it is the subject, it stays in the nominative.

The sentence can be rearranged somewhat, but the original order is very natural.

Original:

• Reći ću ti tačno kada počinje predstava.

Possible variations:

• Tačno ću ti reći kada počinje predstava.
  • puts more focus on exactly
• Kada počinje predstava, reći ću ti tačno.
  • grammatical, but less natural in most normal contexts
• Reći ću ti kada tačno počinje predstava.
  • also natural; the focus shifts slightly toward the timing inside the subordinate clause

Serbian word order is flexible, but clitics like ću and ti still have placement rules, so not every reordering works equally well.

Because they are clitics.

Clitics are small grammatical words that usually:

• do not carry strong stress
• lean on nearby words
• tend to appear in specific positions in the sentence

Here:

• ću = future auxiliary clitic
• ti = unstressed dative pronoun clitic

That is why Serbian often sounds rhythmically compact in sentences like this.

A learner should get used to seeing these short forms frequently:

• ću, ćeš, će...
• mi, ti, mu, joj...
• ga, je, ih...

They are extremely common.

Yes. Serbian reći can correspond to both say and tell, depending on the structure.

In this sentence, because there is an indirect object ti (to you), English usually prefers tell:

• I’ll tell you...

Without an indirect object, English might prefer say in some contexts.

So the Serbian verb is broader, and the best English equivalent depends on the sentence pattern.

A rough guide:

• č sounds like ch in church
• nj is like the ny sound in canyon or Spanish ñ
• j is like English y

So počinje sounds roughly like:

• PO-chee-nye

More exactly, it has three parts:

• po-
• čin-
• -je

And stress in Serbian is not shown in normal spelling, so learners usually pick it up by listening.

Yes, very natural.

It is clear, standard, and idiomatic. A native speaker would have no trouble with it at all.

A slightly more conversational version might be:

• Reći ću ti tačno kad počinje predstava.

But the original sentence is completely normal and correct.