By and Until: Usage Rules, Differences, and Examples
The difference between by and until: rules, examples and explanations
How do you correctly use the words by and until? These two prepositions often confuse English learners. In this article, we will explore their differences, provide usage rules, grammatical specifics, sentence examples, and explanations to help you understand and use these words accurately.
⚡ What does by mean?
The preposition by is used to indicate a deadline or the latest time by which an action must be completed.
Rule: The action must be completed before the specified time.
Meaning: “no later than.”
✅ Examples:
- I need to finish the report by 5 PM.
(This means the report must be completed no later than 5 PM.) - The package will arrive by Friday.
(The package is expected to arrive no later than Friday.) - She must submit the project by the end of the month.
(The project must be submitted no later than the month’s end.)
Note: By indicates the point of completion and does not include events after that point.
🌟 What does until mean?
The preposition until refers to a period during which an action continues up to a specific time.
Rule: The action continues up to (and includes) the specified time.
Meaning: “up to” or “as far as.”
✅ Examples:
- He stayed at the office until midnight.
(He remained in the office up to and including midnight.) - We can’t leave until the meeting is over.
(We must wait for the meeting to finish before we can leave.) - The shop is open until 9 PM.
(The shop remains open up to and including 9 PM.)
Note: Until covers the entire period leading up to the specified time, including that moment.
⚙️ Grammatical Notes
By
Usage:
- Often used with perfect tenses (Present Perfect, Past Perfect, Future Perfect).
Example: The report must have been submitted by now.
(The report should already have been submitted.)
Common structures:
- By + date/time: by tomorrow, by next week.
- By + event: by the end of the day, by the time she arrives.
Until
Usage:
- Frequently used in negative sentences (won’t, can’t, didn’t).
Example: We didn’t leave until it was dark.
(We stayed until darkness.)
Common structures:
- Until + time: until midnight, until Monday.
- Until + event: until she finishes, until the rain stops.
📊 Key Differences Between By and Until
| Feature | By | Until |
|---|---|---|
| Focus | Completion | Duration |
| Time Reference | No later than the time | Continues up to the time |
| Example | Finish it by 6 PM. | Stay here until 6 PM. |
| Meaning | “No later than” | “Up to, as far as” |
💡 How to Remember the Difference
- By = Deadline
Think of by as a dot on a timeline: the action must end before or by this point. - Until = Duration
Visualize until as a line on a timeline: the action continues up to this point.
❗ Common Mistakes
- Replacing until with by:
- I will stay here by 8 PM. ❌
- I will stay here until 8 PM. ✅
- Replacing by with until:
- I need to finish the report until 5 PM. ❌
- I need to finish the report by 5 PM. ✅
✍️ Additional Examples for Practice
- The project must be completed by next Monday.
(The project has to be finished no later than next Monday.) - You can stay at the library until it closes.
(You can remain in the library up to the time it closes.) - Please send the email by the end of the day.
(Ensure the email is sent no later than today.) - We waited until the rain stopped.
(We stayed until the rain ceased.)
📝 Conclusion
By and until have distinct meanings and uses, but they’re easy to differentiate if you remember:
- By focuses on the completion point (deadline).
- Until emphasizes the duration up to a specific moment.
📚 Tip: Use the provided examples to practice creating your own sentences. Avoid common mistakes, and you’ll master these prepositions in no time!