By and until describe a time limit
“By” means “no later than” or “at the point in time when.”
- I need an answer by next Tuesday. (= no later than)
- We should have your car repaired by 4 o’clock this afternoon. (= no later than)
- By the time you read this letter, I’ll already be on my way to California. (= at the point in time when)
“Until” expresses how long an activity has continued or will continue.
- They’ll keep talking until you tell them to be quiet.
- Seth lived at home with his parents until he was 25.
Use “until” with “have” or “give” to express a deadline:
- You have until midnight on April 14 to file your taxes.
- I’m giving you until tomorrow morning to turn in your homework.
NOTE: “Till” is an informal form of “until.”