oneureun yageuni isseoseo neutge toegeunhaeyo.

오늘은 means as for today or simply today.

The particle 은 is the topic particle, so it sets today as the topic of the sentence. It can also give a slight sense of contrast, like:

• Today, I’m leaving work late.
• As for today, I have overtime, so I’m getting off work late.

If you said 오늘이, that would mark today as the subject, which would sound different and usually would not fit this sentence as naturally.

So in this sentence, 오늘은 is very natural because the speaker is talking about today’s situation.

야근 means working overtime, especially working late at night or staying late at work.

It is a very common word in Korean workplace conversation.

Examples:

• 야근해요. = I’m working overtime.
• 야근이 있어요. = I have overtime work / There is overtime work.

In your sentence, 야근이 있어서 means because I have overtime.

In Korean, 야근이 있다 literally means there is overtime, but in natural English it usually means I have overtime or I need to work overtime.

This is a very common Korean pattern:

• 회의가 있어요. = I have a meeting.
• 약속이 있어요. = I have plans/an appointment.
• 야근이 있어요. = I have overtime.

So even though 있다 literally means to exist / to be / to have, in these cases it often works like English have.

The 이 is the subject marker.

In 야근이 있다, the thing that exists is 야근. So 야근 is marked with 이/가.

Structure:

• 야근이 있다 = overtime exists / I have overtime
• 야근이 있어서 = because there is overtime / because I have overtime

This is different from English, where we usually say I have overtime. Korean often expresses this idea with something + 이/가 있다.

있어서 is from 있다 + -어서.

Here, -어서 gives a reason/cause, so 있어서 means:

• because there is
• because I have

So:

• 야근이 있어서 = because I have overtime

In this sentence, it connects the reason to the result:

• 야근이 있어서 → because I have overtime
• 늦게 퇴근해요 → I leave work late

Yes, 야근해서 늦게 퇴근해요 is also possible, but the nuance is a little different.

• 야근이 있어서 늦게 퇴근해요 = I’m leaving work late because I have overtime
• 야근해서 늦게 퇴근해요 = I’m working overtime, so I’m leaving work late

The original sentence focuses on having overtime as the reason.
The version with 야근해서 sounds more like because I’m doing overtime work.

Both are natural, but 야근이 있어서 is especially common when explaining your schedule or situation.

늦게 is the adverb form of 늦다 (to be late).

Since it describes how the speaker leaves work, Korean uses the adverb:

• 늦게 퇴근해요 = leave work late

Compare:

• 늦다 = to be late
• 늦게 = late, in a late way

So:

• 퇴근해요 = leave work
• 늦게 퇴근해요 = leave work late

If you said 늦어요 by itself, it would mean it’s late or I’m late, which is not the same structure.

퇴근하다 means to leave work, to get off work, or to finish work and go home.

So:

• 퇴근해요 = I leave work / I’m getting off work

It is specifically about ending your workday.

Compare:

• 출근하다 = to go to work
• 퇴근하다 = to leave work

So the sentence is talking about the time the speaker finishes work.

퇴근해요 is in the polite present-style ending -아요/어요.

This is one of the most common polite forms in Korean conversation. It is appropriate in many everyday situations.

Here:

• 퇴근하다 → 퇴근해요

Even though it is present tense in form, Korean often uses this form for:

• current facts
• habits
• near-future plans

So in this sentence, 늦게 퇴근해요 can mean:

• I leave work late
• I’m leaving work late
• I’ll get off work late

The exact English translation depends on context.

Yes, in most situations it means I leave work late.

Korean very often omits the subject when it is clear from context. So instead of saying:

• 저는 오늘은 야근이 있어서 늦게 퇴근해요

people usually just say:

• 오늘은 야근이 있어서 늦게 퇴근해요

The listener naturally understands that the speaker is talking about their own situation, unless context suggests someone else.

Some natural translations are:

• I’m getting off work late today because I have overtime.
• I have overtime today, so I’m leaving work late.
• I’m leaving work late today because I have to work overtime.

A more literal breakdown is:

• 오늘은 = as for today
• 야근이 있어서 = because I have overtime
• 늦게 퇴근해요 = I leave work late

So literally, it is something like:

• As for today, because I have overtime, I’m leaving work late.

Yes. 오늘은 can sound like the speaker is talking about today in particular, sometimes with a slight contrast such as:

• normally I don’t leave late, but today I do
• on other days it may be different, but today I have overtime

That contrast does not have to be strong, but it is often felt in sentences with 은/는.

So the sentence can carry a nuance like:

• Today, though, I’m getting off work late because I have overtime.

Yes, that is also possible.

• 오늘은 야근이 있어서 늦게 퇴근해요 = more clearly sets today as the topic, sometimes with a contrastive feel
• 오늘 야근이 있어서 늦게 퇴근해요 = a bit more straightforward, simply today, because I have overtime, I’m leaving work late

Both are natural. Using 은 just adds a topic-marking nuance that is very common in Korean.

Yes, it is polite and very natural for everyday workplace conversation.

If you want to sound more formal, especially in a business setting, you could say:

• 오늘은 야근이 있어서 늦게 퇴근합니다.

That is more formal than 퇴근해요.

But 오늘은 야근이 있어서 늦게 퇴근해요 is already perfectly normal and polite in many real-life situations.