Generally speaking they are used interchangeable, but for some speakers and for some listeners. "I do not know" = you have no knowledge of x "I have no idea" = you have never come across this idea/notion before. If you had not come across the idea or notion before, then logically you will not know. It can be extremely subtle from speaker to speaker and listener to listen, and also upon the context and situation. They are so subtle and so close that it is not worth worrying about.

They both mean the same thing — the speaker does not know. “I have no idea” is more emphatic, like the speaker absolutely does not know and couldn’t even guess. If you simply say you don’t know, it means that you might possibly be able to guess correctly, or you might be able to give an approximation.

Interesting question! For me, it's about the question and what another person is reasonably expected to know. Imagine I ask you what time your local shop opens at. You might answer "I don't know". But there is a good chance that you COULD know the answer because you live in the area and walk by there everyday etc. But if I ask you about the yearly income of that shop you might answer "I have no idea" because you COULDN'T know that information unless you were the manager or accountant of that shop. I hope that helps a little!

Hello! They both mean that the subject doesn't have the answer to something, or what to do about something or they don't have the necessary information about something - it just depends on the context of the situation. "I have no idea" literally means that the person doesn't have the solution or any thought on the matter in their mind. "I do not know" literally means t.hat the person doesn't have the necessary knowledge for that specific thing, or issue, or question. I hope that helps!

Hi You can use both when you have no clue! 😉 When you don't have any information about something you can say: I have no idea! I don't know! I have no clue! Etc.