By and Until / By the time...

By (= Not Later Than)

Use by to say that something happens not later than a certain time.

• I sent the documents today, so they should arrive by Monday. (= on or before Monday)
• We’d better hurry. We have to be home by 5 o’clock. (= at or before 5 o’clock)
• Where’s Sarah? She should be here by now. (= now or before now, so she should already be here)

By sets a deadline: the action is completed at or before that point in time.

Until (= How Long Something Continues)

Use until (or till) to say how long a situation continues.

• Let’s wait until it stops raining. (or till it stops raining)
• I stayed in bed until half past ten.
• I didn’t get up until half past ten.

Until describes the full duration of an action or state, from its start up to a certain time.

By vs. Until — The Key Difference

The difference is about completion vs. continuation.

until (continues up to a time)	by (happens not later than a time)
Joe will be away until Monday. (he’ll be back on Monday)	Joe will be back by Monday. (not later than Monday)
I’ll be working until 11.30. (I’ll stop at 11.30)	I’ll have finished my work by 11.30. (not later than 11.30)

Think of it this way: until tells you when something stops. By tells you the latest time something happens.

By the time… (Future)

Use by the time + present tense to talk about the future. The main clause often uses will or will have done.

• It’s too late to go to the bank now. By the time we get there, it will be closed.
• Hurry up! By the time we get to the cinema, the film will already have started.
• You’ll need plenty of time at the airport. By the time you check in and go through security, it will be time for your flight.

Notice: after by the time, you use a present tense (not will), even though you are talking about the future.

By the time… (Past)

Use by the time + past simple to talk about the past. The main clause often uses the past perfect (had done).

• Karen’s car broke down on the way to the party. By the time she arrived, most of the other guests had left.
• I had a lot of work to do yesterday. I was very tired by the time I finished.
• It took us a long time to find somewhere to park. By the time we got to the cinema, the film had already started.

You can also say by then or by that time:

• Karen finally got to the party at midnight, but by then most of the other guests had left.

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