By, until; By the time

By (+ a time) = not later than:

  • I sent the letter to them today, so they should receive it by Monday.
    (= on or before Monday, not later than Monday)
  • We’d better hurry. We have to be home by 5 o’clock.
    (= at or before 5 o’clock, not later than 5 o’clock)
  • Where’s Sarah? She should be here by now.
    (= now or before now – so she should have already arrived)

We use until (or till) to say how long a situation continues:

  • ‘Shall we go now?’   ‘No, let’s wait until (or till) it stops raining.
  • I couldn’t get up this morning.
    I stayed in bed until half past ten./ I didn’t get up until half past ten.

Compare until and by:

Something continues until a time in the future:

  • David will be away until Monday, (so he’ll be back on Monday)
  • I’ll be working until 11.30. (so I’ll stop working at 11.30)

Something happens by a time in the future:

  • David will be back by Monday.
    (so he’ll be back not later than Monday)
  • I’ll have finished my work by 11.30.
    (= I’ll finish my work not later than 11.30.)

You can say ‘by the time something happens’.

  • It’s too late to go to the bank now. By the time we get there, it will be closed.
    (= the bank will close between now and the time we get there)
  • (from a postcard) Our holiday ends tomorrow. So by the time you receive this postcard. I’ll be back home.
    (= I will arrive home between tomorrow and the time you receive this postcard)
  • Hurry up! By the time we get to the cinema, the film will already have started.

You can say ‘by the time something happened’ (for the past):

  • Karen’s car broke down on the way to the party last night. By the time she arrived, most of the other guests had left.
    (= it took her a long time to get to the party and most of the guests left during this timei
  • I had a lot of work to do yesterday evening. I was very tired by the time I finished.
    (= it took me a long time to do the work, and I became more and more tired during this time)
  • We went to the cinema last night. It took us a long time to find somewhere to park the car. By the time we got to the cinema, the film had already started.

Also by then or by that time:

  • Karen finally arrived at the party at midnight, but by then (or by that time), most of the guests had left.