"in x time" grammar

Hello everyone.

I have a few questions and I’m having trouble finding satisfying answers on Google, I’m hoping someone can help me.

  1. How would I go about saying “The test is in 3 days”, “I will go in 6 months”, etc?
    I know that “ago” is 前に, but 後に gives me “x time later” or “after x time”, so is 「試験は三日間後です。」or 「三日間後には試験です。」also correct if I want to say “The test is in 3 days.” ?

  2. I saw examples where there was no 間 so I don’t know if I should use it or not.

  3. (Assuming the grammar is correct) Is 後 pronounced ご or あと when used like that ?

Crossposting the answers from the Wanikani forums.


Assuming you say all phrases below on Monday:
三日後に試験がある(There is an exam in 3 days) - exam date: exactly Thursday
試験が3日後以降にある(The exam will take place after 3 days) - exam will take place on an unspecified day, after Thursday(including it), so it may be Thursday, Friday, Saturday…

Now, the harder ones:
試験が三日間ある. (The exam will last for three days)
This one is relative. The average hearer will understand it as exam taking place on Tuesday, Wednesday, and Thursday.
If you want to say it will start on Monday, and last to Wednesday you have to say:
試験が 今日から 三日間ある.(The exam will last three days from today.)

試験が3日以内にある (The exam will take place within 3 days) Also relative.
For the average person, the exam will take place on one day: Tuesday, Wednesday or Thursday.
If you want to point, that you start cunting on Monday you say:
試験が 今日(を)含めて3日以内にある。(The exam will take place within three days, including today)
試験が 今日以降3日以内にある。(The exam will take place within three days, starting today)

The blue is a day without an exam, the red is a day with the exam, the red circle is a day with a possibility of the exam taking place.


Thanks a lot for your detailed answer!

後 has many readings, the ones we will focus on are のち、あと、ご。

First of all, if 後 is by itself and then one of particles で、が、を、に etc - you can read it whatever you want(remember that のち will sound very formal, and most likely odd if used in casual speech).

Then STANDARD and MOST COMMON あと construction, and the one you will use:
Verb[た] + 後(で) (usually written in hiragana as あと(で))、Phrase
Noun + の + 後(で) (usually written in hiragana あと(で))、Phrase
AあとでB, after A, B will happen/happened.

By the way, there is pretty commonly used set phrase 後の祭り(あとのまつり), meaning “too late; the jig is up”.

Next, のち which is a VERY FORMAL version of あと/ご, used in some set expressions like 後産(のちざんーafter birth), 後々(のちのちーdistant future, can be read as あとあと though), 後程(のちほどーafterwards, I will see you later. And when talking about weather like 雨のち晴れ(notice it is in hiragana), the clear weather after the rain(btw, it is the title of manga by Bikke).

Verb[た] + 後(に) will be read as のち in FORMAL situation, Phrase
Noun + の + 後(に will be read as のち in FORMAL situation, Phrase
A後に, after A, B will happen/happened.

So, when 後(ご) is used?
It is suffix in kanji compound words like 直後, 午後, 療養後,一時間後, 完成後, 帰国後 etc.