Commonly confused
Fill in vs Fill out
“Fill in” and “Fill out” look alike but pull in different directions. Here is what each one means, with examples — and the difference that learners most often miss.
The key difference
Fill in means write information into the blanks of a form. Fill out means complete a form by writing in the required information.
fill in
- 1
Write information into the blanks of a form
“Fill in your name and address.”
- 2
Temporarily do someone else's job
“Can you fill in for Sam tomorrow?”
- 3
Tell someone the news or details they missed
“Fill me in on what happened.”
fill out
- 1
Complete a form by writing in the required information
“Please fill out this form.”
- 2
Become rounder or more developed in shape
“He's filled out since school.”
- 3
Add details to make something more complete
“Fill out the introduction with examples.”
Stop mixing them up
Sink In turns confusable pairs like this into quick contrast drills, so the right particle becomes automatic.