English UsageGrammar guide
By vs. Until
“By” and “until” both relate events to a time, but they do different jobs. “By” sets the latest acceptable time for completion, while “until” marks how long a state or activity continues.
Use “by” for a deadline (“send it by Friday”); use “until” for something that continues up to a time (“stay until Friday”).
Key details
By Rolesets a deadline meaning not later than a stated time
Core Boundaryby focuses on completion before or at a deadline; until focuses on duration continuing to that point
Until Rolemarks continuation up to a stated time
Further guidance
Deadline Boundary
Use by when something must happen no later than a deadline.
Duration Boundary
Use until when a state or activity continues up to a time.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- By — English Grammar Today (opens in a new tab)Cambridge Dictionary · Deadline use of by meaning not later than a stated time
- Until — English Grammar Today (opens in a new tab)Cambridge Dictionary · Until for continuation up to a time and by-versus-until deadline contrast