Learn Hardcore Indonesian: Kontrak diperpanjang satu tahun. - The contract is extended for one year.

It comes from the base adjective panjang (long). The active verb is memperpanjang (to extend / to lengthen), and the passive form is made with di- + per + panjang → diperpanjang.

So structurally:

panjang = long
memperpanjang (sesuatu) = to make something longer / to extend something
(sesuatu) diperpanjang = something is extended

Why is there no word for “was” or “is” in the Indonesian sentence?

Indonesian usually does not use a separate verb like “to be” (am/is/are/was/were) with verbs.

In Kontrak diperpanjang satu tahun, the passive prefix di- on diperpanjang already signals a verb (“is/was extended”). You don’t add another word for “is/was.”

So:

Kontrak diperpanjang satu tahun.
≈ “The contract is/was extended by one year.”
The tense (“is” vs “was” vs “will be”) comes from context, not from a separate “to be” verb.

How do I say the active version, like “They extended the contract by one year”?

The active form uses memperpanjang:

Mereka memperpanjang kontrak satu tahun.
= “They extended the contract by one year.”

Structure:

Mereka (they) = subject
memperpanjang (extended) = active verb
kontrak (the contract) = object
satu tahun (one year) = duration / amount of extension

Passive vs active pair:

Kontrak diperpanjang satu tahun. = The contract was extended one year.
Mereka memperpanjang kontrak satu tahun. = They extended the contract one year.

Where is the subject in Kontrak diperpanjang satu tahun?

The subject is Kontrak (“The contract”).

Indonesian passive sentences often follow this pattern:
[Patient/thing affected] + [passive verb] + (other info)

So here:

Kontrak = subject (the thing affected)
diperpanjang = passive verb
satu tahun = how long / by how much it was extended

Can I mention who extended the contract? How would I say “The contract was extended by the company for one year”?

Yes. In passive sentences, the agent (the doer) is usually added with oleh (“by”):

Kontrak diperpanjang satu tahun oleh perusahaan.
= “The contract was extended by the company for one year.”

You can also move oleh + agent earlier, but the most straightforward version for learners is:
Kontrak diperpanjang satu tahun oleh perusahaan.

Does diperpanjang mean specifically past tense (“was extended”)? Or can it also mean present/future?

Diperpanjang itself does not mark tense. Indonesian verbs generally have no tense; they show voice (active/passive), but past/present/future comes from context or time words.

Depending on context, Kontrak diperpanjang satu tahun can mean:

“The contract is being extended by one year.”
“The contract has been extended by one year.”
In some contexts (announcements), it can even be understood as “The contract will be extended by one year.”

If you want to be explicit, you can add:

sudah (already): Kontrak sudah diperpanjang satu tahun. = “The contract has already been extended by one year.”
akan (will): Kontrak akan diperpanjang satu tahun. = “The contract will be extended by one year.”

Why is it satu tahun and not “for one year” with a word like “for” or “during”?

The phrase satu tahun (one year) by itself already expresses the amount/duration of the extension, so no extra word is strictly required.

You can say selama satu tahun to emphasize “for a period of one year”:

Kontrak diperpanjang selama satu tahun.
= “The contract was extended for one year.”

But Kontrak diperpanjang satu tahun is normal and natural and typically understood as “by one year / for one year.”

What’s the difference between satu tahun and setahun here?

Both can be used and both mean “one year.”

satu tahun = literally “one year,” a bit more neutral/formal and clear for learners.
setahun = a fused form (se- + tahun), often a bit more casual or conversational.

So you could also say:

Kontrak diperpanjang setahun.
= “The contract was extended for a year.”

In most contexts, satu tahun and setahun are interchangeable.

Is Kontrak diperpanjang satu tahun formal or informal? Where would this sentence be used?

This sentence sounds neutral to slightly formal, and it’s very common in written and spoken Indonesian.

You might see or hear it in:

Official announcements from a company or government
News reports
Contracts and legal documents
Business conversations

In casual speech, you might still hear the same sentence, or a variant like Kontraknya diperpanjang setahun.

What’s the difference between Kontrak diperpanjang satu tahun and Kontraknya diperpanjang satu tahun?

The suffix -nya can function like “the / its / that” depending on context.

Kontrak diperpanjang satu tahun.
= “The contract was extended one year.” (neutral, a bit formal; just states the fact.)
Kontraknya diperpanjang satu tahun.
= “The contract was extended one year.” but with more definiteness / familiarity (“that contract,” “the/its contract we’ve been talking about”). It sounds more conversational.

In many contexts the meaning is the same, but -nya makes it feel more specific to a known contract or more casual.

Is diperpanjang here a verb or an adjective, like “a renewed contract”?

In Kontrak diperpanjang satu tahun, diperpanjang is a verb (“is/was extended”).

If you want to use it like an adjective, you usually put it inside a relative clause:

kontrak yang diperpanjang = “the contract that was extended”
e.g. Ini kontrak yang diperpanjang satu tahun.
= “This is the contract that was extended by one year.”

So:

Kontrak diperpanjang satu tahun. → main verb (The contract was extended one year.)
kontrak yang diperpanjang → describes a noun (contract that was extended).

How do I say “The contract was not extended”?

You negate the verb with tidak:

Kontrak tidak diperpanjang.
= “The contract was not extended.”

If you want to add the duration:

Kontrak tidak diperpanjang satu tahun.
= “The contract was not extended by one year.”

Remember: with verbs (like diperpanjang), use tidak, not bukan.