Tối nay, tôi sẽ đi ngủ sớm vì sáng mai tôi phải đi làm.

Vietnamese very often puts time expressions near the beginning of the sentence to set the scene.

• Tối nay = tonight
• Then the rest of the sentence tells you what happens at that time.

So:

• Tối nay, tôi sẽ đi ngủ sớm... = Tonight, I will go to bed early...

This is very natural in Vietnamese. You could sometimes move the time expression, but putting it first is common and clear.

Both can relate to tonight, but they are not always used in exactly the same way.

• tối nay usually refers to this evening / tonight
• đêm nay refers more specifically to the night itself, often later at night or in a more literary/emotional way

In this sentence, Tối nay sounds very natural because the speaker is talking about their plan for the evening: going to bed early.

So:

• Tối nay, tôi sẽ đi ngủ sớm = very natural
• Đêm nay, tôi sẽ đi ngủ sớm = possible, but less everyday in this context

Sẽ is a future marker. It often works like will in English.

• tôi sẽ đi ngủ sớm = I will go to bed early

Vietnamese does not always need a future marker if the time is already clear, so you may also hear:

• Tối nay, tôi đi ngủ sớm...

Because Tối nay already shows the future, sẽ is not always required. But using sẽ makes the future meaning more explicit.

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

• ngủ = sleep
• đi ngủ = go to sleep / go to bed

In this sentence:

• tôi sẽ đi ngủ sớm means I’ll go to bed early

If you said:

• tôi sẽ ngủ sớm

it would still be understandable, but đi ngủ is more natural when talking about the act of going to bed.

Sớm means early.

In this sentence, it describes đi ngủ:

• đi ngủ sớm = go to bed early

It comes after the verb phrase in Vietnamese, which is very common. Vietnamese adjectives/adverbs often come after the word they modify in cases like this.

Compare:

• dậy sớm = wake up early
• về sớm = come home early
• ăn sớm = eat early

Vì means because.

It introduces the reason:

• vì sáng mai tôi phải đi làm = because tomorrow morning I have to go to work

So the sentence structure is:

• statement + vì
  • reason

You may also see:

• bởi vì = also because, slightly fuller
• do = because of / due to, often more formal depending on context

For everyday speech, vì is very common and natural.

Phải means must / have to.

So:

• tôi phải đi làm = I have to go to work

It expresses obligation or necessity.

A useful comparison:

• tôi đi làm = I go to work / I’m going to work
• tôi phải đi làm = I have to go to work

So phải adds the idea that it is necessary, not just something the speaker happens to do.

Yes, literally it is something like go work, but naturally it means go to work or sometimes just work, depending on context.

• đi = go
• làm = do / work

In everyday Vietnamese, đi làm is a very common expression for going to work.

Examples:

• Mai tôi đi làm. = Tomorrow I’m going to work.
• Anh ấy đang đi làm. = He is at work / He has gone to work.

So even though the wording is different from English, you should learn đi làm as a normal set phrase.

Yes, it can often be omitted if the subject is clear.

Full version:

• Tối nay, tôi sẽ đi ngủ sớm vì sáng mai tôi phải đi làm.

A very natural shorter version:

• Tối nay, tôi sẽ đi ngủ sớm vì sáng mai phải đi làm.

Vietnamese often drops repeated subjects when the meaning is obvious. However, repeating tôi is also completely correct. It can make the sentence clearer or slightly more balanced.

So:

• with the second tôi = clear and explicit
• without it = natural and concise

Vietnamese verbs do not conjugate like English verbs.

That means the verb form stays the same:

• đi ngủ
• đi làm

Time and meaning are shown by:

• time words like tối nay, sáng mai
• markers like sẽ
• modal words like phải

So instead of changing the verb, Vietnamese adds other words around it.

This is a major difference from English and something learners usually find helpful once they get used to it.

Sáng mai means tomorrow morning.

• sáng = morning
• mai = tomorrow

In Vietnamese, the order is often:

• part of day + day reference

So:

• sáng nay = this morning
• sáng mai = tomorrow morning
• chiều mai = tomorrow afternoon
• tối mai = tomorrow evening

This may feel reversed compared with English, but it is the normal Vietnamese order.

Yes, but the meaning becomes less specific.

• sáng mai = tomorrow morning
• ngày mai = tomorrow

In this sentence, sáng mai is more precise because it explains why the speaker wants to sleep early tonight: they have work specifically in the morning.

If you say:

• vì ngày mai tôi phải đi làm

it means because I have to work tomorrow, which is fine, but not as specific.

The comma is common and helpful, but in informal writing it may be omitted.

• Tối nay, tôi sẽ đi ngủ sớm... = neatly separates the time phrase
• Tối nay tôi sẽ đi ngủ sớm... = also acceptable

The comma is especially useful when a sentence begins with a longer time or topic phrase. It makes the sentence easier to read.

Yes. In everyday speech, Vietnamese speakers often shorten it.

For example:

• Tối nay tôi đi ngủ sớm vì sáng mai phải đi làm.

This sounds very natural in conversation.

You could also hear even more casual versions depending on context, especially if tôi is already understood:

• Tối nay đi ngủ sớm, vì sáng mai phải đi làm.

That said, the original sentence is clear, correct, and perfectly natural.

Tones matter a lot in Vietnamese, so it helps to notice some key words:

• tối — falling-rising tone
• sẽ — hỏi/ngã-family tone depending on dialect spelling/pronunciation pattern; in standard spelling it carries ~
• ngủ — hỏi tone
• sớm — acute rising tone
• vì — huyền low-falling tone
• sáng — acute rising tone
• phải — hỏi tone

A learner should especially be careful not to flatten the tones, because words with different tones can become different words.

Also notice the rhythm:

• Tối nay, tôi sẽ đi ngủ sớm / vì sáng mai tôi phải đi làm.

It naturally breaks into two parts:

1. the main action
2. the reason

That can help both pronunciation and comprehension.