Ako ne kasniš, stižeš rano na posao.

Because Serbian usually drops subject pronouns when they are already clear from the verb form.

• kasniš = you are late / you’re running late
• stižeš = you arrive

The ending -š already shows 2nd person singular, so ti is not necessary.

You could say Ako ti ne kasniš, ti stižeš rano na posao, but that sounds emphatic, as if contrasting you with someone else.

In Serbian, the present tense is often used for general truths, habits, and regular if-conditions, just like in English:

• Ako ne kasniš, stižeš rano na posao.
• If you’re not late, you arrive at work early.

This sounds like a general rule or something that usually happens.

If you wanted to talk about one specific future situation, Serbian would more naturally use a future-oriented form, for example:

• Ako ne budeš kasnio, stići ćeš rano na posao.
• If you’re not late, you’ll arrive at work early.

So the original sentence sounds habitual / general, not like a one-time prediction.

Here, ako means if and introduces a condition:

• Ako ne kasniš = If you’re not late

That is its basic and most common meaning.

In this sentence, ako sets up the condition, and the second clause gives the result:

• condition: Ako ne kasniš
• result: stižeš rano na posao

Because in Serbian, the negative particle ne is normally written separately from the verb.

So:

• kasniš = you are late / you’re running late
• ne kasniš = you are not late / you’re not running late

This is standard with most verbs.

A few very common verbs behave differently, such as:

• nisam
• nemam
• neću

But with kasniš, the normal form is ne kasniš.

Because Serbian verbs belong to different conjugation patterns.

• kasniti → kasnim, kasniš, kasni...
• stizati → stižem, stižeš, stiže...

So even though both mean you here, the stems and endings follow different verb classes.

A native English speaker often expects a more uniform pattern, but Serbian verbs can change in different ways depending on the infinitive and stem.

Not quite.

• stižeš comes from an imperfective verb and often suggests a regular, repeated, or ongoing pattern
• stigneš comes from a perfective verb and often points to a single completed arrival

So in this sentence:

• Ako ne kasniš, stižeš rano na posao
  = a general habit or usual result

If you said:

• Ako ne zakasniš, stigneš rano na posao

that would sound more like a specific completed outcome, though in practice native speakers may choose slightly different wording depending on context.

For a learner, the simplest takeaway is:

• stižeš = good for habitual / general
• stigneš = more one-time / completed

Because rano here is an adverb, not an adjective.

It describes how you arrive:

• stižeš rano = you arrive early

Adverbs in Serbian do not agree with nouns in gender, number, or case.

Compare:

• rani voz = an early train
  Here rani is an adjective and must agree with voz.
• stižeš rano = you arrive early
  Here rano is an adverb modifying the verb.

Because na posao is the normal idiomatic expression for to work / to the workplace in this kind of sentence.

• ići na posao = to go to work
• stići na posao = to arrive at work

Here na is followed by the accusative because it expresses direction toward a destination:

• posao is the accusative form here

Compare:

• Idem na posao. = I’m going to work.
• Na poslu sam. = I’m at work.

So:

• na posao = movement toward work
• na poslu = location at work

Using u posao would usually not sound right in this meaning.

Because Ako ne kasniš is a subordinate clause that comes before the main clause.

So Serbian punctuation follows the same logic as English here:

• Ako ne kasniš, stižeš rano na posao.

The comma separates:

• the if-clause
• from the main clause

This is standard and expected in writing.

Yes, Serbian word order is fairly flexible, but the original order is the most neutral.

Neutral version:

• Ako ne kasniš, stižeš rano na posao.

Possible variations:

• Ako ne kasniš, rano stižeš na posao.
• Na posao stižeš rano ako ne kasniš.

These are still understandable, but the focus changes slightly.

The original sentence is the best basic version for a learner because it sounds natural and straightforward.

This is a very common learner question.

• kasniti = to be late / to be running late
• zakasniti = to end up late / to arrive late / to be late once, as a completed event

In your sentence:

• Ako ne kasniš sounds like if you’re not running late
• Ako ne zakasniš would sound more like if you don’t end up being late

So kasniti fits well in a general, habitual statement.

Very roughly:

• kasniti = state/process
• zakasniti = completed result

Mostly like a general fact or practical observation.

It sounds like:

• If you’re not late, you get to work early.

So it has the feel of a regular consequence, not really a threat.

Depending on tone, it could also sound mildly ironic, because the statement is so obvious. But grammatically, it is simply a normal conditional sentence describing what usually happens.