Saya lupa PIN kartu debit saya.

Because the two saya do different jobs:

• the first saya = I (the subject)
• the second saya = my (possession)

Indonesian often uses the same word for I/me and my, depending on position in the sentence.

So:

• Saya lupa ... = I forgot ...
• ... kartu debit saya = my debit card

This is completely normal in Indonesian.

In Indonesian, possessives usually come after the noun.

So:

• kartu saya = my card
• PIN kartu debit saya = literally PIN debit card my

That word order may feel backwards to an English speaker, but it is standard Indonesian structure.

It is a noun phrase built step by step:

• PIN = PIN
• kartu debit = debit card
• kartu debit saya = my debit card
• PIN kartu debit saya = the PIN of my debit card / my debit card PIN

A useful way to think of it is:

• PIN
  • of
    • my debit card

Indonesian often leaves the of relationship unspoken.

It can cover all of those, depending on context.

Indonesian verbs do not change form for tense the way English verbs do. So lupa itself does not tell you whether the action is present or past.

Depending on context, Saya lupa PIN kartu debit saya could mean:

• I forgot my debit card PIN
• I’ve forgotten my debit card PIN
• I forget my debit card PIN (less likely in most situations)

If you want to make the time clearer, Indonesian usually adds time words or aspect markers, for example:

• Saya sudah lupa ... = I’ve already forgotten ...
• Tadi saya lupa ... = Earlier I forgot ...
• Sekarang saya lupa ... = Right now I can’t remember ...

Yes, in everyday grammar it functions like the main predicate of the sentence.

However, learners sometimes notice that lupa can behave a bit differently from a very action-like verb such as makan (eat). It often expresses a state of not remembering, not just the action of forgetting.

That is why translations like forgot and don’t remember can both fit, depending on context.

Because Indonesian does not normally use articles like a/an/the.

So Indonesian can simply say:

• PIN kartu debit saya

and the listener understands from context whether it means:

• a PIN
• the PIN
• my debit card PIN

In this sentence, context makes it naturally definite/specific.

Because Indonesian usually puts the main noun first and the modifier after it.

So:

• kartu debit = debit card
• kartu kredit = credit card
• rumah sakit = hospital
• bahasa Indonesia = Indonesian language

English often uses modifier + noun, but Indonesian commonly uses noun + modifier.

Yes. That is a natural, more informal version.

Compare:

• Saya lupa PIN kartu debit saya. = polite/neutral/formal
• Aku lupa PIN kartu debitku. = casual/informal

A few notes:

• aku is less formal than saya
• -ku is a possessive suffix meaning my

So:

• debitku = my debit
• more naturally, kartu debitku = my debit card

Try not to mix levels of formality too randomly. For example, Saya lupa PIN kartu debitku is understandable, but stylistically mixed.

Usually, no—not unless the context already makes the ownership obvious.

Compare:

• Saya lupa PIN kartu debit saya. = clear: it is my debit card PIN
• Saya lupa PIN kartu debit. = sounds incomplete or less clear, more like I forgot the PIN of the debit card

If everyone already knows you are talking about your own card, Indonesian speakers may shorten things in conversation, but the full version with the second saya is safer and clearer for learners.

It is better to say Saya lupa PIN kartu debit saya without dengan.

For lupa, Indonesian normally allows a direct object:

• Saya lupa namanya.
• Saya lupa alamatnya.
• Saya lupa PIN kartu debit saya.

There is also lupa akan ..., but that sounds more formal or literary in many contexts.

So the most natural everyday version here is the one without a preposition.

Only the PIN.

The object of lupa is the whole phrase PIN kartu debit saya, so what is forgotten is the PIN, not the card.

If you wanted to say you forgot to bring the card or left it somewhere, you would use different wording, for example:

• Saya lupa membawa kartu debit saya. = I forgot to bring my debit card.
• Kartu debit saya hilang. = My debit card is lost.

Yes, PIN is commonly used in Indonesian.

It is a borrowing from English and is very normal in banking/ATM contexts. So PIN kartu debit sounds natural.

You may also hear people say:

• nomor PIN

Even though PIN already includes the idea of a number, that kind of redundancy is common in many languages, including Indonesian.

Yes, it is natural and correct.

A few very natural alternatives are:

• Saya lupa PIN kartu debit saya.
• Saya lupa nomor PIN kartu debit saya.
• Aku lupa PIN kartu debitku. (informal)

The original sentence is a good standard version.