I’ve heard a lot of English learners misuse in or after. I understand why it can be confusing. Most likely, your native language does not have a similar distinction. However, mixing up in or after will instantly sound wrong to a native speaker. Making such a mistake is similar to using the wrong tense, and that metaphor is closer to reality than you might think. I’ve discussed many other small differences between English words, but this one will sound very wrong if you make a mistake.
“In” is about a future time specifically in relation to now
Essentially, if you are talking about a future after this moment, you must use “in.”
I will be home in one hour.
= I will arrive one hour after now.
I am going to be busy in 20 minutes, so tell me what you need now.
= 20 minutes after this moment will not be a good time.
All of time expressions have a point of comparison. For “in,” it is always now.
“After” is about a future time compared to anytime that is not now
If you are telling a story, and you need to compare something to a later time from the past (or the future), you must use “after.”
Also, it is okay to say the time first and then “after” as long as it is a number, not an event:
YES: after one hour, one hour after, after twenty minutes, twenty minutes after
NO: dinner after, school after, my homework after
First, he ate his lunch. Then, he washed his plate five minutes after.
= He washed his plate five minutes after his lunch.
Later, I will study some vocabulary. After an hour of studying, I will take a break.
= Studying will stop one hour after my future study begins.
The point of comparison should never be now when you use the word “after.” The point of comparison can be any other time in the past or future.
In or after compared:
I am going to travel to Britain. In two months, I am going to see Australia.
= The trip to Britain will happen at an unknown time. There is also a trip to Australia two months after now. However, it is unclear how those are connected in this sentence.
This sounds like someone listing their plans.
I am going to travel to Britain. Two months after, I am going to see Australia.
= The trip to Britain will happen first. Two months will pass from the time of the person’s arrival in Britain, and this person will go to Australia.
Someone is explaining their trip because there is a direct time connection between the two events.
In summary
- in – in relation to now
- after – in relation to the past or future
RULE OF THUMB: You will only see the word “after” when talking about time in history books. You should only use “in” when talking about your plans for the rest of today, which is compared with this moment in time. However, if you compare the time relation of two of your future plans, you will use “after.”
Be careful with these two because misusing can instantly show you are not a native speaker. While many of the small differences in word choice depend on what natives prefer to discuss, which I have discussed in a YouTube video, whether you choose in or after will be the same for all native speakers. Because of this, be sure to practice this grammar point often to sound as native and natural as possible.
