​WHICH WORD?

By / Until

Used with "time"
for specific situations related to “time”.

by

  • not later than
    (a specified time) 

  • something could be completed before
    ​(a specific time)
EXAMPLES:
​
  1. The operation will be completed by 10:00 pm. It might be completed before 10:00 p.m. 

  2. We will arrive in Miami by 6:00 a.m. We might arrive sooner, but for sure not after 6:00 a.m.  

  3. I’ll be there by 5. I might arrive earlier than 5, but not after.  
    ​
  4. I hope to learn English by the time I finish the university. Maybe I will learn it before.

until

  • up to
    (a particular time)
    ​
  • a period of (specific time) 
EXAMPLES:
​
  1. I’m going to study English tonight until 10, and then I will go out for a beer. 
    From now –> 10 you will be studying.

  2. He will study for the test for 3 hours.  From 3:00 p.m until 6:00 p.m.

  3. I will stay at the party until it is over.

  4. I will study English until I learn it.
Note: By

Usually answers the question “When” in the future tense.

  • When will the project be finished?  
    By November.

  • When will you arrive at the party?  
    By 6 for sure.

  • When will you call me?  
    By Thursday.  I promise.
    ​
​NOTE: Until

Usually answers the question "How long"

  • How long will you be working on the project?  
    Until November.

  • How long will it take you to finish the report?    
    Until 3 this afternoon.

  • How long were you in New York?    
    Until it started snowing then I went to Florida.