Learn Hardcore Croatian: Ako je bolesna i sutra, posjetit ću je poslije posla. - If she is sick tomorrow too, I will visit her after work.

In Croatian, future conditions introduced by Ako normally use the present tense in the if-clause. The result clause then uses Future I: ću/ćeš/će/ćemo/ćete/će + infinitive. So Ako je bolesna i sutra, posjetit ću je... is the standard pattern. You can also say Ako bude bolesna i sutra... (a slightly more formal/emphatic variant). Avoid Ako će biti... in standard Croatian.

Is it correct to say Ako će biti bolesna i sutra?

Not in standard Croatian. In if-clauses you normally use the present (Ako je...) or bude (Ako bude...), not će biti. So prefer:

Ako je bolesna i sutra, ...
Ako bude bolesna i sutra, ...

What exactly does i in i sutra mean here?

Here i means also/too/still. Ako je bolesna i sutra = “If she is sick tomorrow too.” Without i, Ako je bolesna sutra just says “If she is sick tomorrow,” without the “too/again” nuance.

Can I move i so it’s Ako je i sutra bolesna?

Yes. Both are fine:

Ako je bolesna i sutra (as in the original)
Ako je i sutra bolesna (arguably a bit more idiomatic, because i directly precedes the word it modifies)

Be careful: Ako je sutra i bolesna sounds odd here. If you want “even if,” use čak i ako: Čak i ako je sutra bolesna...

Why is it written posjetit ću and not posjetiti ću?

When the clitic ću comes after the infinitive, the infinitive drops its final -i:

posjetit ću (correct)
posjetiti ću (incorrect)

If ću comes before the infinitive, you keep -i:

Ja ću posjetiti (je).

Where does the object pronoun je go? Could I say ću je posjetiti?

Clitics (like ću, je) can’t start a clause; they need a “host” before them. So:

Correct: Posjetit ću je poslije posla.
Correct: Sutra ću je posjetiti.
Incorrect to start the clause with: Ću je posjetiti.

In your sentence, you can say:

Ako je bolesna i sutra, posjetit ću je poslije posla.
Ako je bolesna i sutra, ja ću je posjetiti poslije posla.

There are two je’s—are they the same word?

They look the same but aren’t:

First je = 3rd person singular of biti (“is”): je bolesna = “is sick.”
Second je = clitic pronoun “her” (accusative): posjetit ću je = “I will visit her.”

Can I use ju instead of je for “her”?

Yes. je and ju are both standard feminine accusative clitics in Croatian. je is the default; ju is common and can help avoid confusion with the verb je. All are acceptable:

Posjetit ću je poslije posla.
Posjetit ću ju poslije posla. For emphasis (stressed form), use nju: Posjetit ću nju (a ne njega).

What case is posla, and why not posao?

Poslije governs the genitive case. posao (NOM) becomes posla (GEN):

poslije posla = “after work” Similarly, nakon also takes genitive: nakon posla.

Is poslije posla the only way to say “after work”?

Other natural options:

nakon posla (very common)
poslije radnog vremena (“after working hours,” a bit more formal/specific)

Note: posle posla is Serbian; in standard Croatian prefer poslije/nakon.

What about aspect—why posjetiti and not posjećivati?

Posjetiti is perfective (a single, completed visit), which fits a one‑off plan in the future. If you mean repeated or ongoing visits, use the imperfective posjećivati:

Posjetit ću je poslije posla. = I’ll visit her (once).
Posjećivat ću je poslije posla. = I’ll be visiting her (repeatedly).

Can I put the main clause first and what happens to the comma?

Yes:

Posjetit ću je poslije posla ako je bolesna i sutra. When the ako-clause comes second, you normally don’t use a comma. When it comes first, you do:
Ako je bolesna i sutra, posjetit ću je poslije posla.

Could I replace Ako je bolesna i sutra with Ako bude bolesna i sutra?

Yes. Ako bude bolesna i sutra is also correct and slightly more formal or cautious. It can suggest a condition still to be confirmed at that future time. Both versions are fine in everyday speech.

If the person were masculine or plural, what would change?

Masculine singular: Ako je bolestan i sutra, posjetit ću ga poslije posla.
- adjective: bolestan, object pronoun: ga
Feminine plural: Ako su bolesne i sutra, posjetit ću ih poslije posla.
- verb: su, adjective: bolesne, pronoun: ih
Masculine plural: Ako su bolesni i sutra, posjetit ću ih poslije posla.