Tôi sẽ nhắn bạn sau giờ làm.

Sẽ marks the future. It is similar to will in English.

So:

• Tôi nhắn bạn sau giờ làm = I message you after work / I’ll message you after work, depending on context
• Tôi sẽ nhắn bạn sau giờ làm = I will message you after work

In everyday Vietnamese, people often leave out sẽ if the time expression already makes the future clear. But adding sẽ makes the future meaning more explicit.

In Vietnamese, many verbs do not need a separate word like English to before the person receiving the action.

So:

• nhắn bạn = message you
• literally, it is more like message you than message to you

This is normal Vietnamese sentence structure. The verb nhắn is followed directly by the person being contacted.

Nhắn usually means to send a message, to text, or to leave a message, depending on context.

In this sentence, it most naturally means:

• text
• message
• contact by message

It is less likely to mean a phone call. If you specifically want to say call, you would usually use gọi.

For example:

• Tôi sẽ gọi bạn sau giờ làm. = I’ll call you after work.
• Tôi sẽ nhắn bạn sau giờ làm. = I’ll message/text you after work.

Here, bạn means you.

Although bạn can mean friend in some contexts, it is also a very common second-person pronoun in Vietnamese, especially in neutral and polite conversation.

So in this sentence:

• Tôi = I
• bạn = you

A native English speaker often finds this confusing at first because the same word can serve different roles depending on context.

Tôi is a common way to say I in Vietnamese. It is fairly neutral and polite.

Compared with English, Vietnamese pronouns depend a lot on relationship, age, and social situation. So tôi is not the only word for I.

For example, depending on who is speaking, someone might say:

• mình
• em
• anh
• chị

But tôi is a safe, standard choice for learners, especially when you do not know the relationship details.

Sau giờ làm means after work or after working hours.

Breaking it down:

• sau = after
• giờ làm = work time / working hours

So the phrase refers to the time after the speaker finishes work.

Depending on context, English might translate it as:

• after work
• after I get off work
• after working hours

You could, but it sounds different and less natural in this situation.

• sau giờ làm = after work / after work hours
• sau khi làm việc = after working / after doing work

Sau giờ làm is the natural everyday expression for after work.
Sau khi làm việc sounds more literal and is not the usual way to say this in casual speech.

Another very common alternative is:

• Tôi sẽ nhắn bạn sau khi tan làm. = I’ll message you after I get off work.

Yes. Vietnamese word order is somewhat flexible, especially with time expressions.

The original sentence:

• Tôi sẽ nhắn bạn sau giờ làm.

A natural variation is:

• Sau giờ làm, tôi sẽ nhắn bạn.

Both mean the same thing. The second version puts the time first for emphasis, like:

• After work, I’ll message you.

Sometimes, yes.

Vietnamese often drops subjects when they are clear from context. So in conversation, someone might simply say:

• Sẽ nhắn bạn sau giờ làm.
• Nhắn bạn sau giờ làm nhé.

However, for learners, including tôi is helpful because it makes the sentence complete and clear.

Yes, it is natural and understandable.

That said, in casual speech, native speakers may use slightly more conversational versions, such as:

• Tôi nhắn bạn sau giờ làm nhé.
• Sau giờ làm tôi nhắn bạn nhé.
• Tan làm rồi tôi nhắn bạn.

Adding nhé can make the sentence sound softer and friendlier.

Nhắn by itself can already mean message or send a message.
Nhắn tin is more specific and often means text/message by phone.

So:

• Tôi sẽ nhắn bạn sau giờ làm. = I’ll message you after work.
• Tôi sẽ nhắn tin cho bạn sau giờ làm. = I’ll text/message you after work.

Both are fine. Nhắn tin can sound a bit more explicit, especially if you want to emphasize texting.

Because with nhắn, Vietnamese often allows the receiver to come directly after the verb.

So this is natural:

• nhắn bạn

You may also hear:

• nhắn cho bạn

Both are possible, but nhắn bạn is more direct and compact.
Adding cho can make the relationship a little more explicit, like message to you, but it is not required here.

The original sentence is already neutral and polite enough.

More casual:

• Mình sẽ nhắn bạn sau giờ làm.
• Tớ sẽ nhắn cậu sau giờ làm.
  (used between friends, depending on region and relationship)

Softer/politer:

• Tôi sẽ nhắn bạn sau giờ làm nhé.

More formal:

• Tôi sẽ liên lạc với bạn sau giờ làm.
  This sounds more like I will contact you after work than specifically message you.

So the level of formality depends mostly on the pronouns and the final particles, not just the verb.