#1. Apparent expressions

Informal and casual, for kids or your friends:

• 좋은 아침 (Joeun achim [tʒoɯn achim])
• 좋은 아침이야. (Joeun achimiya [tʒoɯn achimija])

Informal but polite, for adults:

• 좋은 아침이에요. (Joeun achimieyo [tʒoɯn achimiejo])

Honorific speech, formal and polite:

• 좋은 아침입니다. (Joeun achimimnida [tʒoɯn achimimnida])

However, it’s awkward. Koreans generally don’t use greetings like that in daily life.

Korean is one of languages that doesn’t have time-spesific greetings unlike English, German, Spanish, Chinese, and even Japanese.

Then, what greetings do they use?

#2. Real live expressions

Informal and casual, for kids or your friends:

• 안녕? (Anneyong? [annjʌŋ])

Informal but polite, for adults:

• 안녕하세요. (Annyeonghaseyo [annjʌŋɦasejo])

Honorific speech, formal and polite:

• 안녕하십니까. (Annyeonghasimnikka [annjʌŋɦaɕimnik͈a])

These are for all of good morning, good afternoon, and good evening. They don’t distinguish greetings time-specifically as I said earlier.

#3. Another “good morning” in Korean — when you wake up

However, one of greetings is actually translated into “good morning,” but not in English. Here it is:

• 잘 잤어? (Jal jasseo? [tʒal dʒas͈ʌ])
• 안녕히 주무셨어요? (Annyeonghi jumusyeosseoyo [annjʌŋɦi dʒumuɕ͈jʌs͈ʌjo])
• 안녕히 주무셨습니까? (Annyeonghi jumusyeosseumnikka [annjʌŋɦi dʒumuɕ͈jʌs͈ɯmnik͈a])

This is for someone who woke up after sleep. So, it can be “good morning” in the morning.

There is one form of speech style that you must be careful of.

• 잘 잤니? (Jal janni? [tʒal dʒanni]) — good morning. (after wake-up)

‘-니’ form of interrogatives is what you have to beware of. This is only available when you’re saying to someone absolutely lower than you in social level and age, such as adults to children.

Thus, if you’re young, you NEVER can use -니 form to your elders.

This is because the -니 form is of 하게체 (hage style). It’s not that easy to understand how to use exactly to non-Koreans as this style is highly cultural.

Hope it helps.