Meaning trap

fill in

complete a form

to write the necessary information on a form or document.

phrasal verbB1core

Don't mix these meanings

Same phrase, different job.

complete a form

to write the necessary information on a form or document.

fill in (substitute for someone)

Another meaning of 'fill in' is 'substitute for someone'; compare the examples to keep the meanings separate.

Notice where the phrase sounds natural.

Please fill in this application form before your interview.daily life
In my country, when you open a bank account, you have to fill in several forms with your personal details.IELTS speaking

Pattern: fill in [object]

WrongPlease fill the form.

RightPlease fill in the form. / fill out the form.

For forms, use 'fill in' (BrE) or 'fill out' (AmE) — bare 'fill' means make full.

Patternfill in [object]

Choose the version that sounds natural in speech.

Stiff Kindly complete the application document in its entirety.

Natural Just fill in the form.

'Fill in' is what everyone says for completing a form (BrE); the formal version is a bureaucrat's note.

Words that usually travel with it.

'Fill out' is also used in American English with the same meaning.

fill in (substitute for someone) — Another meaning of 'fill in' is 'substitute for someone'; compare the examples to keep the meanings separate.