Commonly confused
Fill in vs Fill out
“Fill in” and “Fill out” look alike but pull in different directions. Here is the quick way to tell them apart — with examples, the mistake to avoid, and a check.
Which one do you mean?
For forms they mean the same — fill in is mainly British, fill out mainly American. Fill in also means substitute for someone, or add missing detail.
Fill in
Complete a form (UK), add missing information, or cover for someone.
Fill out
Complete a form (US).
fill in
- 1
Write information into the blanks of a form
- 2
Temporarily do someone else's job
- 3
Tell someone the news or details they missed
Correct use
“Leo filled in a delivery form at the parcel shop.”
Leo wrote the required details in the delivery form.
fill out
- 1
Complete a form by writing in the required information
- 2
Become rounder or more developed in shape
- 3
Add details to make something more complete
Correct use
“Please fill out this form.”
Please complete this form by writing in the details.
Common mistake
Please fill the form.
Please fill in the form. / Please fill out the form.
A form needs fill in (UK) or fill out (US).
Test yourself
“Leo filled in a delivery form at the parcel shop.” What does it mean?
Sink In — iOS & Android
Stop mixing them up
Sink In turns confusable pairs like this into quick contrast drills, so the right particle becomes automatic instead of a guess.
- Learn the pattern behind dozens of verbs at once — not one-off translations.
- Spaced repetition (SM-2) brings each meaning back right before you forget.
- Four practice modes train recall and discrimination, not just recognition.
