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By vs. Until: What's the Difference?

Edited by Janet White || By Harlon Moss || Published on November 19, 2023
"By" indicates a deadline or the end of a specific time period, while "until" signifies the duration up to a certain point in time.

Key Differences

"By" and "until" are both prepositions that deal with time, but they serve different purposes. "By" sets a specific endpoint or deadline, while "until" emphasizes the continuation of an action or situation up to a particular time.
If you're asked to complete a task "by" a certain date, it means the task should be finished on or before that date. On the other hand, if you're told to wait "until" a certain date, it means you should continue waiting and not act before that date arrives.
"By" often indicates a period of time within which an action should be completed. For instance, "I'll send the email by 5 PM." Conversely, "until" suggests that something continues up to a point in time, as in "Stay indoors until the rain stops."
Imagine a library scenario. If the librarian says, "Return the book by Monday," it denotes a deadline. However, if the librarian says, "You can keep the book until Monday," it indicates the duration for which you can possess the book.
"By" is not limited to denoting time; it can also indicate means or agency, such as "sent by mail." "Until," on its part, remains time-focused, often emphasizing the full duration of a time period.

Comparison Chart

Basic Function

Indicates an endpoint or deadline
Signifies duration up to a certain point

Time Connotation

Specific moment or end of a time frame
Continuation up to a point in time

Example Usage

"Finish the task by Friday"
"Work on the task until Friday"

Extension to Other Contexts

Can indicate means or agency (e.g., "by car")
Primarily time-focused


Doesn't denote ongoing action
Emphasizes ongoing action up to a specific time

By and Until Definitions


Denoting agency or action.
The novel was written by Jane Austen.


Denoting a continuous action up to a specific time.
She studied until midnight.


Referring to the means or method.
I traveled by train.


Expressing a condition for an event not happening.
Don't open the letter until Christmas.


Referring to intervals or increments.
Increase the volume by 10%.


Up to the point in time mentioned.
Wait here until I return.


Indicating the end of a time period.
The project must be done by Tuesday.


Indicating the end of a waiting period.
The show won't start until 8 PM.


Indicating proximity or location.
The shop is by the river.


Indicating the period of validity.
The offer is valid until June 30th.


Close to; next to
The window by the door.


Up to the time of
We danced until dawn.


With the use or help of; through
We came by the back road.


If I have a deadline, which word should I use?

Use "by" to indicate a deadline, as in "Submit the report by Friday."

What's the primary difference between "by" and "until"?

"By" indicates a deadline, while "until" signifies duration up to a certain time.

Does "until" always refer to the future?

Primarily, but it can refer to any duration ending at a specific past or future point.

Can "by" refer to location?

Yes, as in "The house by the lake."

Can "by" be used for intervals?

Yes, as in "Reduce the sugar by half."

Which word emphasizes an ongoing action?

"Until" emphasizes ongoing action, as in "She read until midnight."

If something is valid for a period, which word should I use?

Use "until" to indicate validity, as in "Offer valid until December 31st."

If I refer to the agent of an action, which word should I use?

Use "by" to indicate agency, as in "Painting by Van Gogh."

Can I say "Wait here by I return"?

No, the correct phrasing is "Wait here until I return."

Can "by" indicate a method of doing something?

Yes, as in "I traveled by plane."

Can "until" indicate a condition?

Yes, as in "Don't speak until spoken to."

How does "by 5 PM" differ from "until 5 PM"?

"By 5 PM" means no later than that time; "until 5 PM" means continuously up to that time.

If something continues for a duration, which word fits best?

"Until" fits best, as in "The shop is open until 9 PM."

Does "by" always indicate a strict deadline?

Typically yes, but context matters. "By" suggests on or before a time.

Can "until" be used with past events?

Yes, as in "She lived there until 2010."

Which preposition indicates increments or measures?

"By," as in "Cut the ingredients by half."

Which word indicates proximity?

"By" indicates proximity, as in "Sit by me."

Does "by" always relate to time?

No, "by" can indicate means, agency, or location too.

Which word is more versatile in its uses?

"By" is more versatile, with applications beyond just time.

Which word would suggest a waiting period?

"Until" suggests waiting, as in "Wait until the lights turn off."
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.

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