What's the difference between 'fill in' and 'fill out'?

Both mean to complete a form. 'Fill out' is more common in American English. 'Fill in' is used in both US and UK English. They are interchangeable for forms.

Can I say 'fill in someone' to mean inform them?

No. The correct order is 'fill someone in.' Example: 'Can you fill me in on the meeting?' Not 'fill in me.'

Is 'fill in' formal enough for work emails?

Yes. 'Fill in' works in both casual Slack messages and formal emails. For very formal documents, you might prefer 'complete' or 'provide.'

How do I use 'fill in' when talking about replacing someone?

Use 'fill in for' + person. Example: 'I'll fill in for the PM while she's on vacation.' This means you will do her tasks temporarily.

What's the past tense of 'fill in'?

The past tense is 'filled in.' Example: 'I filled in the form yesterday.' The participle is also 'filled in.'

Can I use 'fill in' for code or technical documentation?

Yes. You can fill in comments, fill in documentation, fill in a config template, or fill in placeholder values in code.

What Does "Fill In" Mean at Work?

Commonness
Versatility
Formality	CasualFormalNeutral
Spoken ↔ Written	SpokenWrittenBoth
Directness ↔ Diplomatic	DirectDiplomaticNeutral
Region

Say it like this

✓Can you fill in the acceptance criteria on this ticket?

✓I'll fill in for Sarah while she's on vacation.

✓Let me fill you in on what happened in the meeting.

✓Please fill in all required fields before submitting.

✓I need to fill in some details on the PR description.

Real examples

Standup

"I still need to fill in the test cases for this feature before it's ready for review."

Slack message

"Hey, can you fill in the deployment steps in the runbook? They're missing."

GitHub PR

"Please fill in the PR template with the testing instructions."

Jira ticket

"Fill in the acceptance criteria so QA knows what to test."

Retrospective

"We should fill in the action items from last sprint before we start."

Sprint planning

"Let's fill in the story points for these new tickets."

Pair programming

"Can you fill me in on what this function is supposed to do?"

Don't say this

✕Can you fill the form?

✓Can you fill in the form?— 'Fill in' is the correct phrasal verb. 'Fill' alone means to make something full (like a container).

✕Please fill in me about the meeting.

✓Please fill me in about the meeting.— When 'fill in' means to inform someone, the person goes between 'fill' and 'in'.

✕I will fill in the blanks later.

✓I will fill in the details later.— 'Fill in the blanks' is correct but sounds like a test. In work contexts, 'fill in the details' sounds more professional.

Other forms

base form

fill in

"I need to fill in the form."

third person

fills in

"She fills in the required fields."

past tense

filled in

"I filled in the ticket yesterday."

present participle

filling in

"I'm filling in for the tech lead this week."

past participle

filled in

"The template has been filled in."

Often used with

fill in the detailsAdd missing information to a document or ticket.

fill in a formComplete a form by entering required data.

fill in for someoneTemporarily do someone else's job or task.

fill someone inGive someone information they missed.

fill in the gapsProvide missing pieces of information or context.

Similar words

completeMore formal. Used in official documents and instructions.

provideMore formal. Often used in written requests.

addSimpler and more casual. Works for any missing content.

updateImplies changing existing information, not just adding new.

cover forOnly for the 'replace someone temporarily' meaning.

Opposites

leave blankskipomitdeleteremove

Practice

Try it

4 quick exercises

Choose the most natural sentence

1. You need a teammate to add details to a Jira ticket. What do you say?

Can you fill the ticket?Can you fill in the ticket details?Can you filling in the ticket?

Find the error

2. Please fill in me on what happened in the sprint planning.

fill in mewhat happenedin the sprint

Complete the sentence

3. I'll ___ for the scrum master while she's on leave.

Make this more natural

4. Please complete the missing information in the PR description.

More words

update complete submit template required fields acceptance criteria documentation

Questions

Quick poll

Have you said "fill in" in a standup this week?

Want more structured practice like this? Our English for Programmers course covers real workplace English in depth.

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