-잖아요 vs -거든요: What Is the Difference?

Key facts

• -잖아요 means "you know" or "as you know." It treats the information as shared, and it can carry a hint of impatience.
• -거든요 means "you see" or "the reason is." It offers a reason or background that is new to the listener.
• 잖아요 comes from -지 않아요, and both endings attach to the verb stem and take tense: 말했잖아요, 안 먹었거든요.
• Both are polite 요 endings, but -잖아요 can sound blaming, especially to an older person.

What you'll learn

• Choose -잖아요 or -거든요 for five test sentences and state the deciding rule in one sentence.
• Build both endings from verbs, adjectives and 이다, in the present and the past.
• Place a -거든요 sentence after the statement it explains.
• Avoid the most common error: using -잖아요 for news the listener has not heard.

Before you start: you should know the polite ending -아요/-어요 and how to form the verb stem. If you want the full rules for each pattern first, read -잖아요 and -거든요.

What Is the Difference between -잖아요 and -거든요?

The difference is the speaker's assumption about the listener. With -잖아요, the speaker assumes that the listener knows the fact, or should know it. With -거든요, the speaker assumes the listener does not know the fact, and offers it as an explanation. English has similar tools: "you know" (-잖아요) versus "you see" or "the thing is" (-거든요).

Two sentences show the contrast:

• 오늘 휴일이잖아요. (oneul hyuirijanayo.) = "Today is a holiday, you know." Both people know the date, and the speaker uses it to explain why the street is empty.
• 못 가요. 오늘 약속이 있거든요. (mot gayo. oneul yaksogi itgeodeunyo.) = "I can't go; I have an appointment today." The listener did not know about the appointment, and the speaker gives it as the reason.

Both sentences end with a polite 요, and both give a reason. The difference lies in who is expected to know the reason. The next section puts the differences into a table.

-잖아요 vs -거든요: Side-by-Side Table

The table lists the points learners need most. Each row gives one answer for each pattern.

The table shows that the two endings share the polite level and the "reason" job, but split on what the listener already knows. Each one gets a close look next.

When Do You Use -잖아요?

Use -잖아요 when you remind the listener of a fact they know or should know. The ending is a contraction of -지 않아요 ("isn't it the case that ..."), and it often carries a small push: "Don't you remember?"

To remind. 지난주에 말했잖아요 (jinanjue malhaetjanayo) = "I told you last week, you know." The listener forgot, and the speaker reminds them. The word is the past stem 말했 plus 잖아요.

To give a shared reason. 비가 오잖아요. 우산 가져가세요 (biga ojanayo. usan gajyeogaseyo) = "It's raining, you know. Take an umbrella." Both of you can see the rain, so the reason is shared.

To agree or persuade. 이 식당 유명하잖아요 = "This restaurant is famous, you know." The speaker uses the shared fact to back a suggestion.

To get attention. The word 있잖아요 [읻짜나요] is an opener like "you know, ..." or "listen,": 있잖아요, 저 질문이 있어요. It is a separate use that tries to catch the listener's attention.

To build the ending, remove 다 from the dictionary form and add 잖아요. The stem never changes, because 잖 begins with a consonant:

The ending is easy to build, but it can cause trouble. It can sound as if you are blaming the listener. First, look at the second ending.

When Do You Use -거든요?

Use -거든요 when you give a reason, an explanation or background that the listener does not know. The reason usually comes after the thing it explains. The ending sounds like "the thing is ..." or "you see ...".

To explain a result. 배가 고파요. 아침을 안 먹었거든요 (baega gopayo. achimeul an meogeotgeodeunyo) = "I'm hungry. I didn't eat breakfast, you see." The first sentence is the result, and the second is the new reason.

To explain a past action. 어제 일찍 잤어요. 많이 피곤했거든요 (eoje iljjik jasseoyo. mani pigonhaetgeodeunyo) = "I went to bed early yesterday. I was very tired, you see."

To explain a refusal. 못 가요. 오늘 약속이 있거든요 = "I can't go. I have an appointment today." The listener could not know about the appointment.

To give background before a question. 제가 내일 시간이 있거든요. 같이 갈래요? (jega naeil sigani itgeodeunyo. gachi gallaeyo?) = "I have time tomorrow, you see. Shall we go together?" The speaker shares background and then asks.

To explain yourself. 저 한국어 공부해요. 한국 드라마를 좋아하거든요 = "I study Korean. I like Korean dramas, you see."

To build the ending, remove 다 and add 거든요. The stem never changes:

The ending is easy to build, and the harder part is to tell which one a sentence needs. The next section looks at cases where both fit.

Can You Use Both in the Same Sentence?

You can use both in one conversation, and they often appear in turn. A natural dialogue shows how:

• A: 왜 안 와요? (wae an wayo?) = "Why aren't you coming?"
• B: 오늘 바쁘거든요. 어제 말했잖아요. = "I'm busy today, you see. I told you yesterday, you know."

B first gives the reason (new to A at that moment) and then reminds A that it was said before.

The same fact can use either ending, depending on what the speaker thinks the listener knows. 오늘 휴일이잖아요 assumes the listener knows. 오늘 휴일이거든요 assumes the listener does not know: it suits a tourist who asks why the shop is closed. The fact is the same, and only the assumption about the listener changes.

The overlap is limited to this switch of assumption, so the next section turns it into a rule.

Which One Should You Pick? a Simple Rule of Thumb

Ask what the listener knows. Use this four-step check.

1. Find the fact. Say it in English: "Today is a holiday."
2. Ask whether the listener knows it. Did they hear it, see it, or learn it before?
3. Choose the ending. If yes, use -잖아요. If no, use -거든요.
4. Check the person. If the listener is older or senior, be careful with -잖아요, because it can sound as if you are blaming them.

Apply the check to "I'm full. I ate a lot." The listener did not see you eat, so use 배불러요. 많이 먹었거든요. Apply it to "It's cold. It's winter." Both of you know it is winter, so use 추워요. 겨울이잖아요.

If you cannot decide, -거든요 is the safer choice with a new listener or an older person, because it makes no claim about what they know. The next section looks at the places where learners slip.

What Mistakes Do Learners Make with These Two?

Learners most often assume that the listener knows or does not know. Four mistakes appear again and again.

1. Using -잖아요 for news. 저 내일 시험이 있잖아요, said to someone who has never heard of the exam, sounds as if they should know. Say 저 내일 시험이 있거든요.
2. Using -거든요 for the obvious. 지금 비가 오거든요, said while both of you watch the rain, sounds odd. Say 지금 비가 오잖아요.
3. Using -잖아요 with elders. 지난번에 말씀드렸잖아요 can sound like a complaint, even with polite words. With a teacher or a boss, choose a gentler form such as 지난번에 말씀드렸는데요.
4. Putting the reason first. A -거든요 sentence that explains a result normally comes after it. 아침을 안 먹었거든요. 배가 고파요 sounds abrupt. Say 배가 고파요. 아침을 안 먹었거든요. When -거든요 opens with background instead, the next sentence usually adds 그래서 or asks something, as in 제가 내일 시간이 있거든요. 같이 갈래요?

Use this checklist when a sentence feels wrong: Does the listener know this? Is the reason after the result? Is the listener older than me? The remaining differences are edge cases.

When Do the Two Endings Work Differently?

The two endings work differently with tone, with questions and with sentence position.

• Tone. -잖아요 carries feeling: impatience, persuasion or a friendly "you know." -거든요 is calmer and sounds like explaining. Tone of voice matters a lot for both.
• Questions. Neither is a normal question. A rising tone on -잖아요 is not the usual way to ask. If you need to check what someone knows, use -지요, which is covered in a separate comparison.
• Sentence position. -거든요 can stand alone as an answer: 왜 안 가요? — 바쁘거든요. -잖아요 usually needs the shared fact to be clear from the context.
• One honest limit. This page covers the polite spoken endings. The casual forms -잖아 and -거든 follow the same logic, and formal writing uses other patterns, such as -기 때문이다.

Since the choice depends on the listener, practice with short exchanges is the best way to learn it.

Practice: Choose the Right Pattern

Try the five items before you read the answer key.

1. Choose. "Today is a holiday, you know." Both people know the date. Which fits: 휴일이잖아요 or 휴일이거든요?
2. Choose. You explain to a friend why you are late. Complete: 길이 막혔___. (잖아요 / 거든요)
3. Fix the error. A learner says 저 어제 한국에 왔잖아요 to a stranger. What is the problem, and how can it be fixed?
4. Build. Make both endings for 바쁘다.
5. Reorder. Put in order: 아침을 안 먹었거든요. / 배가 고파요.

Answer key

1. 휴일이잖아요. Both people know the fact.
2. 거든요. The friend does not know the reason yet.
3. 잖아요 assumes the stranger knows. Say 저 어제 한국에 왔거든요.
4. 바쁘잖아요 and 바쁘거든요.
5. 배가 고파요. 아침을 안 먹었거든요. The result comes first.

A final test: if you could add "as you know" in English, use -잖아요. If you could add "you see" or "the thing is," use -거든요.

What Should You Learn Next?

After this comparison, study each ending on its own and then compare -지요. This page compares the two endings but does not teach every use of either one.

1. Read the full lesson on -잖아요, which covers the casual form and tone.
2. Read the full lesson on -거든요, which covers background and refusal uses.
3. See how a softer reminder differs in -지요 vs -잖아요.
4. Check the intermediate list at Intermediate Grammar to see where both endings sit among the B1 lessons.
5. Compare other confusing pairs at Confusing Grammar Compared.

With these steps, the choice between -잖아요 and -거든요 becomes automatic: decide what the listener knows, then add the matching ending.

Frequently Asked Questions

What is the difference between -잖아요 and -거든요?

-잖아요 reminds the listener of something both of you know: 오늘 휴일이잖아요 means "today is a holiday, you know." -거든요 gives a reason or background that the listener does not know yet: 오늘 약속이 있거든요 means "I have an appointment today, you see." The question is what the listener already knows.

Can I always replace -잖아요 with -거든요?

No. The same fact can take either ending, but the message changes. 오늘 휴일이잖아요 assumes the listener knows the date. 오늘 휴일이거든요 assumes they do not. Swapping the endings changes who is expected to know, so use the one that matches the situation.

Which one sounds more natural in speech?

Both are very common in spoken Korean. -잖아요 is frequent among friends and colleagues who share context, and -거든요 is frequent when someone explains a reason or gives background. With an older or senior listener, -거든요 is usually the safer choice because -잖아요 can sound blaming.

Which one appears more often on TOPIK?

No reliable count is available, so this site makes no claim. Both endings appear in dialogues at intermediate level, where the speaker's assumption about the listener decides the answer. Reading the context for what each person already knows is the most useful habit for test items.

What is the quickest rule to remember?

Ask what the listener knows. If they know it, or should, use -잖아요 and think "as you know." If it is news to them, use -거든요 and think "you see." Put the -거든요 sentence after the result it explains, and be careful with -잖아요 toward elders.

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