# be on duty

CEFR B1 · Fixed phrase

Source: https://englishreference.com/word/be-on-duty
Updated: 2026-07-26

## Definition

to be at work and responsible for your job at a specific time.

For teachers: to be engaged in one's professional obligations or assigned tasks during a scheduled period. This phrase functions as a predicative adjective phrase following the copula 'be'.

## Examples

- The nurse will be on duty until eight tonight.
- I cannot join you for lunch because I will be on duty at the security desk all afternoon.
- The commanding officer required at least two senior guards to be on duty throughout the duration of the diplomatic summit.

## Pitfalls

- Not "The doctor is in duty today." but "The doctor is on duty today." — the fixed expression requires the preposition 'on' rather than 'in'.

## Usage notes

- usually refers to jobs that involve shifts or public service, such as police, medical staff, or soldiers.
- Teaching tip: contrast with 'off duty' to show how the prepositional change flips the meaning; you can also mention 'active duty' for military contexts.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.