The rule, as people use it

Both words point at a time in the future, but they draw different pictures.

"Until" is a line. Something keeps going, without a break, and stops at that time. "I'll work until five" means you're working at one, at three, at four fifty, and then you stop. The verb has to be something that can last: stay, wait, work, sleep, be open.

"By" is a deadline. Something happens once, at any moment before that time, and not later. "I'll finish the report by five" means it could be done at two or at four thirty. Five is the last possible moment. The verb is usually a single event: finish, arrive, send, decide, pay.

So the quick test is this: is the action a line or a dot? A line that ends at a time, "until". A dot that must land before a time, "by". Compare "Can you stay until nine?" with "Can you be here by nine?" The first asks you not to leave. The second asks you not to arrive late.

Examples

Tap a sentence to hear it. Say it after the voice.

Fill the gap

Type the missing words, then check. The full sentence plays when you get it.

  1. 1

    The library stays open (9 p.m.) on weekdays.

  2. 2

    I have to hand in my essay (Monday morning).

  3. 3

    Let's keep walking (we find) a place to eat.

  4. 4

    Our guests should be here (seven), so start cooking.

  5. 5

    He didn't learn to drive (he was thirty).

  6. 6

    Could you fix the heater (the weekend)? It's freezing.

  7. 7

    I'm staying in Edinburgh (the end of August).

  8. 8

    (the time) the movie ended, everyone was asleep.

Practice · 3 min

Plan tomorrow with both words. Write each sentence, then say them out loud.

  • I'm going to sleep until ___ .
  • I need to leave home by ___ .
  • I'll be at work, at school or at home until ___ .
  • I have to finish ___ by ___ .
  • Tomorrow night, I'm going to stay up until ___ .
  • By next Sunday, I want to ___ .

Say it today

Use it once in a real conversation before tomorrow. Out loud counts, even to yourself.