“Let’s Call It a Day” Means “Let’s Stop for Now”

“Let’s call it a day” is commonly used after people have been working or doing an activity for some time. It proposes stopping for today, or simply stopping for the present. It does not mean literally naming something “a day”, and it does not necessarily mean giving up permanently.

For example, colleagues checking figures late in the afternoon might say: “It’s nearly six. Let’s call it a day and finish the figures tomorrow.” The phrase sounds like a shared decision to wrap up, rather than the blunt instruction “Stop working”. It is natural in Australian, British and American English. If the intention is to end a project, partnership or relationship altogether, “call it quits” may be closer, though context still matters.

https://www.collinsdictionary.com/dictionary/english/call-it-a-day