There is no ‘to be’ in Indonesian. Sometimes learner use ‘adalah’ as to be, this is not wrong, but not always right.

Adalah has several meaning:

1. Identical with: example – Clark Kent is Superman (Clark Kent adalah Superman)
2. Has same meaning with – April is the fourth month (April adalah bulan keempat)
3. Belong to a group or classes – She is a doctor (Dia adalah seorang dokter)

From the definition above, it seems like ‘adalah’ acts like ‘to be’ or ‘is’. But it is not always the case.

Let’s check the tenses in English one by one.

Simple Present Tense

For simple present tense, adalah may sometimes act as ‘to be’. All of the examples above are simple present tense. But you need to remember, ‘adalah’ should only be used if the meaning falls into those 3 categories.

If it is not, then you should just omit the ‘to be’. You can also omit ‘to be’ when it is the 3^rd category (belong to a group or classes). Example:

1. That house is red – Rumah itu merah
2. They are neighbors – Mereka tetangga
3. She does not lie – Dia tidak berbohong
4. I do not like it – Saya tidak suka itu

Present Continuous Tense

In this form, you can omit the ‘to be’ and just add ‘sedang’ before verb. Example:

1. My mother is cooking dinner – Ibu saya sedang memasak makan malam
2. You are not sleeping – Kamu tidak sedang tidur

Present Perfect Tense

In this form, you can omit the ‘to be’ and add ‘sudah’ before verb or ‘belum’ if it is negative sentence. Example:

1. I have read that book – Saya sudah membaca buku itu
2. I have not read that book - Saya belum membaca buku itu
3. She has finished her homework – Dia sudah menyelesaikan tugas rumahnya

Present Perfect Continuous Tense

Omit ‘to be’ and add ‘sudah’ before verb or ‘belum’ if it is negative sentence. Example:

1. She has been working in this company for two years – Dia sudah bekerja di perusahaan ini selama dua tahun
2. I have been waiting for five minutes – Saya sudah menunggu selama lima menit
3. My daughter has not been visiting us since last year – Anak perempuan saya belum mengunjungi kami sejak tahun lalu

I don't know how you to do it, but you always bring up things that I don't understand. Thank you very much. It was very useful :)

Simple Past Tense

Since Indonesian does not have ‘to be’, to differentiate past tense and present tense, we use the word ‘dulu’ or ‘tadi’. ‘Dulu’ is for something that happened long ago, and ‘tadi’ for something happened not so long ago, usually for something happened in the same day. If the ‘to be’ carries the meaning which falls into the 3 categories of ‘adalah’ meaning, you should add ‘adalah’ after ‘dulu’ or ‘tadi’.

Example:

1. She was an actress – Dia dulu adalah seorang aktris
2. I was there – Saya tadi di sana
3. I did not understand – Saya tadi tidak mengerti

If there is no to be, you can either use ‘tadi’ or ‘dulu’ or omit it and add the time when it happened, or just omit it:

1. I went to school at 8 – Saya pergi ke sekolah jam 8
2. I went to Germany – Saya dulu pergi Jerman
3. She read that book this morning – Dia membaca buku itu pagi ini
4. She read that book – Dia membaca buku itu

All of these are correct. In a conversation, it is easier to throw the word ‘dulu’ or ‘tadi’ in a sentence. But in a text like when you are reading books or any text, you should see the context of the sentences to know when the action is happening. This applied to any sentences that talking about the past.

Past Continuous Tense

Similar with present continuous tense, we need to add ‘sedang’ to indicate that the action is still continue to happen. And similar with simple past tense, we can add ‘dulu’ or ‘tadi’ to indicate that the action was happening in the past (or we can omit it).

Example:

1. Tina was drinking tea – Tina tadi sedang minum teh
2. My friend was playing video game – Teman saya tadi sedang bermain video game
3. The cat was running in the street – Kucing sedang berlari di jalan

Past Perfect Tense

Similar with present perfect tense, we need to add ‘sudah’ (or ‘belum’ if negative sentence) to show that the action has been happening for a while. And similar with simple past tense, we can add ‘dulu’ or ‘tadi’ to indicate that the action was happening in the past (or we can omit it).

Example:

1. I had eaten breakfast before I left for work – Saya tadi sudah  sarapan sebelum saya berangkat kerja.
2. They had studied this before you came – Mereka dulu sudah mempelajari ini sebelum kamu datang.
3. I came here after you had left – Saya datang ke sini setelah kamu sudah pergi.

Past Perfect Continuous Tense

Similar with present perfect continuous tense, we need to add ‘sudah’ (or ‘belum’ if negative sentence) to show that the action has been happening for a while. And similar with simple past tense, we can add ‘dulu’ or ‘tadi’ to indicate that the action was happening in the past (or we can omit it).

Example:

1. I had been working for three years when I got the promotion – Saya dulu sudah bekerja selama tiga tahun ketika saya mendapatkan promosi
2. The program had been working well since 1945 before it was terminated – Program itu sudah bekerja dengan baik sejak 1945 sebelum diberhentikan.

Since Indonesian does not have a strict structure of tenses like in English grammar, to define how “to be” should be translated in Future Tense is a bit tricky. This is how I usually translate sentences as natural as possible, as how natives talk. Let me know if you have any questions or comments.

Simple Future Tense

To indicate that an event happens in the future, we use the word ‘akan’ before a verb. Akan is literally translated as “will” or “going to”.

Example:

1. I will eat later – Saya akan makan nanti
2. I am going to go to Bali next week – Saya akan pergi ke Bali minggu depan.
3. I will not cry – Saya tidak akan menangis

Future Continuous Tense

Theoretically, just like Past Continuous or Present Continuous, you can add ‘sedang’ to indicate that an action is progressing. But most of the time, Indonesian treats Future Continuous Tense like Simple Future Tense.

Example:

1. I will be eating at 8 am tomorrow – Saya akan makan pada jam 8 pagi besok
2. She will be dancing all night tonight – Dia akan berdansa sepanjang malam malam ini

Future Perfect Tense

For an action that should have finished in the future, we usually say “seharusnya sudah” + verb + time in the future when the action finished.

Example:

1. I will have finished this book by the time you arrive – Saya seharusnya sudah menyelesaikan buku ini ketika kamu datang
2. He will have arrived next week – Dia seharusnya sudah datang minggu depan

When you are counting how many days (or times) you have been doing an action, you can omit the word “seharusnya”. Example

1. We will have lived here for 2 months next Saturday – Kita sudah tinggal di sini selama 2 bulan Sabtu depan.

Future Perfect Continuous Tense

This tense is also similar with Future Perfect.

For a summary:

1. If it already happened or it happened and still continuing to happen for some time now, use "sudah" + verb
2. To differentiate the present, past, and future, explain the timing of when this action happened or use adverb of time.
3. If you are not sure when something is happening in the past, you can use the word "dulu" for a long time ago, or "tadi" for something that happened within 24 hour.
4. For something that is expected to happen in the future, use "akan" + verb
5. For an action that should have finished in the future, use "seharusnya sudah" + verb