What is the difference between (if any) "fill in for" and "sit in for"? Are they used interchangeably ? If yes, then what is more likely to be used?

Like a teacher is ill so another teacher comes to teach the class for a day:

Your teacher is ill, so I'll be filling in/sitting in for him today.

(The teacher may or may not sit)

The Manager is busy, so another person had to attend the meeting.

The Manger is busy, so I'm filling in/sitting in for him today.

(And all sorts of such contexts......) Thank you:)

1 Answer 1


In US English they are almost interchangeable. "Sit in for" generally means literally sitting in the chair that would be used by the missing person. "Fill in for" means to temporarily take over that person's duties. "Sit in for" means literally taking that person's physical place while taking over that person's duties.

I might "fill in for" my manager by attending a meeting. I might "sit in for" my manager by moving to the head of the table and conducting that meeting.

  • So in the first sentence, will it be "sit in for" or "fill in for"? Commented Sep 3, 2019 at 0:40
  • @It'saboutEnglish I asked my wife who is a school teacher. She says she would use "fill in". Commented Sep 3, 2019 at 1:47
  • 1
    Hi I had another question: > We were quite a ways back stuck in traffic yesterday. _____________________________________________ Actually it is about a few people who take the same bus each day and the bus travels the same route each day. Yesterday they got to their stop late because they were held up by traffic and today they got to their stop on time and thus said this, as at this time yesterday they were stuck in traffic. Does this sentence sound natural to you? Most of the people don't find it natural.….. Commented Sep 5, 2019 at 19:30
  • It does sound natural to me, especially given the context (standing there, perhaps pointing "back", knowing it's a daily cycle). But it could be a regional thing for sure (not sounding natural to others). Commented Sep 5, 2019 at 20:24

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