Kalau perut saya masih kosong, saya tidak bisa fokus menulis laporan di kantor.

Here kalau means if.

So:

Kalau perut saya masih kosong, ... = If my stomach is still empty, ...

It is very similar to jika, but there is a tone difference:

• kalau = common, natural, everyday
• jika = more formal, more written, sometimes more careful-sounding

So this sentence sounds natural in normal conversation and ordinary writing.

In Indonesian, possession is usually shown by putting the owner after the noun.

So:

• perut saya = my stomach
• rumah saya = my house
• nama saya = my name

This is the normal pattern:

noun + pronoun/person

So perut saya is the correct and natural order.

Literally:

• masih = still
• kosong = empty

So perut saya masih kosong literally means my stomach is still empty.

In natural English, that usually means something like:

• I still haven’t eaten
• I’m still hungry
• My stomach is still empty

This is a very understandable and natural way to express the idea in Indonesian.

Both are possible, but they are slightly different in nuance.

• saya lapar = I am hungry
• perut saya masih kosong = my stomach is still empty

The second one feels a bit more descriptive and physical. It emphasizes the condition of the stomach, not just the feeling of hunger.

So:

• Saya lapar, saya tidak bisa fokus... = simpler
• Kalau perut saya masih kosong... = a little more vivid

Because the sentence has two clauses, and each clause has its own subject:

1. Kalau perut saya masih kosong
2. saya tidak bisa fokus menulis laporan di kantor

In Indonesian, it is very common to repeat the subject for clarity, especially across clauses.

English often does this too:

• If my stomach is still empty, I can’t focus...

Could Indonesian sometimes omit the second saya in context? Yes, in casual speech, sometimes. But the full version with both saya is clear and completely normal.

Because tidak is used to negate:

• verbs
• adjectives
• verb-like expressions

Here it negates bisa:

• tidak bisa = cannot / am not able to

Use bukan mainly to negate nouns or noun phrases.

Compare:

• Saya tidak bisa fokus. = I can’t focus.
• Itu bukan laporan. = That is not a report.

So in this sentence, tidak is the correct choice.

Bisa here means can / be able to.

So:

• saya tidak bisa fokus = I can’t focus

A useful thing to know is that bisa can also mean poison in other contexts, but in everyday sentences like this one, it clearly means can.

Examples:

• Saya bisa datang. = I can come.
• Dia tidak bisa tidur. = He/She can’t sleep.

Because Indonesian often links verbs more directly than English does.

In English, we say:

• focus on writing
• be able to write

In Indonesian, a structure like this is very normal:

• fokus menulis laporan

This means something like:

• focus on writing a report
• focus while writing a report

You do not always need an extra word like to or on.

You may also hear other versions, such as:

• fokus untuk menulis laporan
• fokus pada penulisan laporan

But in many everyday contexts, fokus menulis laporan sounds natural and efficient.

Di kantor means at the office or in the office.

• di = at / in
• kantor = office

It tells us the location of the action menulis laporan.

So the sentence means that the person cannot focus on writing the report at the office.

A key point:

• di is a preposition here, so it is written separately: di kantor
• this is different from di- as a prefix in passive verbs, which is written together

Compare:

• di kantor = at the office
• ditulis = written

The most natural English understanding is focus on writing the report.

In Indonesian, verb combinations can be broader and less tightly marked than in English. So fokus menulis laporan is understood as focusing on the activity of writing the report.

A learner should usually interpret it as:

• focus on writing the report

not literally word-for-word.

Yes. Indonesian often allows the kalau clause either before or after the main clause.

Original:

• Kalau perut saya masih kosong, saya tidak bisa fokus menulis laporan di kantor.

Also possible:

• Saya tidak bisa fokus menulis laporan di kantor kalau perut saya masih kosong.

Both mean essentially the same thing.

The version with kalau first puts more emphasis on the condition.

It is very natural to use a comma there, especially in writing, because the conditional clause comes first:

• Kalau perut saya masih kosong, saya tidak bisa fokus...

This works much like English:

• If my stomach is still empty, I can’t focus...

In very informal writing, people may leave it out, but using the comma is clear and standard.

It is natural and understandable.

It sounds like a clear, standard sentence. A native speaker might also say similar alternatives depending on style, for example:

• Kalau saya belum makan, saya tidak bisa fokus menulis laporan di kantor.
• Kalau saya lapar, saya tidak bisa fokus menulis laporan di kantor.

These may sound a bit simpler in everyday speech, but your original sentence is still good Indonesian.