Learn Hardcore Croatian: Čim budemo u zgradi, nazvat ću te s mobitela. - As soon as we are in the building, I will call you from my phone.

Present tense to talk about the future
- Kad dođeš, nazvat ću te. – When you come, I’ll call you.
Or future II (budem, budeš, bude, budemo…
- past participle, sometimes shortened)
- Čim budemo u zgradi, nazvat ću te.
  Literally: As soon as we (will) be in the building, I’ll call you.

So čim budemo u zgradi is the standard way of saying this.
The form čim ćemo biti u zgradi is common in everyday speech, but it is considered non‑standard or less correct in formal Croatian.

What tense or form is budemo exactly?

Budemo is the 1st person plural of future II (often called future perfect) of the verb biti (to be).

Full future II form would be: budemo bili (when we will have been).
In practice, with biti, Croatians usually drop the participle bili, so you just hear:
- Kad budemo u Zagrebu…
- Čim budemo u zgradi…

Functionally, in this sentence it means “when we are / once we are (in the building)” but from the point of view of the main future action (nazvat ću te), it’s something that will be reached first, then the call follows.

So:

budemo = future II of biti, used in a time clause referring to the future.

Could I say Čim ćemo biti u zgradi, nazvat ću te instead?

You will hear people say this, but in standard Croatian grammar it is considered incorrect or at least non‑standard.

Rules for clauses with čim / kad / dok referring to the future:

Standard: use present tense or future II in the subordinate clause.
- Čim budemo u zgradi, nazvat ću te. (future II)
- Kad dođem kući, nazvat ću te. (present with future meaning)
Non‑standard but frequent in speech:
- Čim ćemo biti u zgradi, nazvat ću te. (future I inside the time clause)

If you want a very natural, simple alternative that avoids future II, you can say:

Čim uđemo u zgradu, nazvat ću te. – As soon as we enter the building, I’ll call you.
Here uđemo is present tense form used with future meaning.

What is the difference between čim and kad?

Both introduce time clauses, but:

kad = when, neutral about how quickly something follows
- Kad budemo u zgradi, nazvat ću te. – When we are in the building, I’ll call you.
čim = as soon as, stresses immediate succession
- Čim budemo u zgradi, nazvat ću te. – As soon as we are in the building, I’ll call you (immediately).

So čim adds the nuance “immediately after / the moment that…”. In many contexts you can use kad instead, but it sounds slightly less urgent or less immediate.

Why is it u zgradi and not u zgradu?

Because u zgradi describes being inside the building (a location), not movement into it.

Croatian uses different cases with u:

Accusative (direction, movement into somewhere)
- Idemo u zgradu. – We are going into the building.
Locative (location, being in somewhere)
- Mi smo u zgradi. – We are in the building.

In the sentence Čim budemo u zgradi, you are talking about the state of already being inside, so you use the locative:

u zgradi (locative singular, feminine)

What exactly does nazvat ću te mean, and what is the base verb?

Nazvat ću te = I will call you (on the phone).

Base (dictionary) verb: nazvati – a perfective verb, “to call (once, to make a call)”.
Future I is formed as: ću
- infinitive → ću nazvati.
  In speech, the infinitive often loses the final -i:
  - nazvati → nazvat → nazvat ću.

So:

nazvati (perfective) – to place a call (a single, completed action)
zvati / zvati (imperfective) – to be calling, to call repeatedly, etc.
- Zvat ću te kasnije. – I’ll be calling you / I’ll give you a call later. (more informal)

In the sentence, nazvat ću te is the most neutral and standard way to say I’ll call you.

Why is it nazvat ću te and not ću te nazvat(i) or te ću nazvat(i)? Are those wrong?

All of these are grammatically possible, because Croatian word order is quite flexible, but there are preferences:

Neutral, most common:
- Nazvat ću te s mobitela.
Also possible but marked/emphatic or stylistically different:
- Nazvat ću te. (same as neutral)
- Ja ću te nazvati. (emphasis on I)
- Te ću nazvati s mobitela. (strong emphasis on you in particular, sounds a bit literary or dramatic)

The usual rule is that little pronouns and auxiliaries (ću, te, ga, mi, se etc.) form a “clitic cluster” that tends to occupy the second position in the clause.
In nazvat ću te, the cluster (ću te) comes right after the first stressed element nazvat. That’s why it sounds so natural.

So ću te nazvati or te ću nazvati aren’t strictly wrong, but they are less neutral and often used only for emphasis or in specific stylistic contexts.

Why is mobitela used with s? What case is it?

In s mobitela, mobitela is in the genitive singular.

s (or sa before some consonants) often means “from (the surface / device / source of something)”:
- s mobitela – from the mobile (phone)
- s televizora – from the TV
- s interneta – from the internet
- s krova – from the roof

So nazvat ću te s mobitela literally is:

I’ll call you *from (my/the) mobile phone.*

The pattern is: s + genitive to express origin or source.
That’s why you have mobitela (genitive), not mobitel (nominative) or mobitelom (instrumental).

Could I also say nazvat ću te mobitelom instead of s mobitela?

You can, but it doesn’t sound as natural for “a phone call”.

s mobitela (genitive) = from the mobile phone (as a source/device of the call).
This is the normal way to say it when talking about calls.
mobitelom (instrumental) usually means “with the mobile phone (as a tool/means)”:
- Otključala je vrata mobitelom. – She unlocked the door with her phone.
- Udario ga je mobitelom. – He hit him with a mobile.

You might hear nazvat ću te mobitelom, but to native ears it often sounds a bit odd, as if the phone were a physical tool (like a hammer) rather than the source of the connection.

So for “call you on/from my cell”, stick with:

nazvat ću te s mobitela (most natural), or simply
nazvat ću te (if the device is obvious from context).

Why is there no explicit word for “we” in budemo?

Croatian is a pro‑drop language: subject pronouns (ja, ti, on, mi, vi, oni) are often omitted because the verb ending already shows the person and number.

budemo = we will be (1st person plural is clear from the ending -emo)
So Čim budemo u zgradi already means “As soon as we are in the building” without needing mi.

You could say:

Čim mi budemo u zgradi, nazvat ću te…
but that adds extra emphasis on we (“as soon as we are in the building…”), which isn’t necessary in the neutral version.

Can I replace Čim budemo u zgradi, nazvat ću te s mobitela with a simpler version that feels more “present tense”?

Yes. A very natural, slightly simpler alternative that avoids future II is:

Kad uđemo u zgradu, nazvat ću te s mobitela.
When we enter the building, I’ll call you from my mobile.

Or even:

Čim uđemo u zgradu, nazvat ću te.

Here uđemo is present tense form (1st person plural) used with future meaning, which is perfectly standard in time clauses in Croatian.