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BY vs. UNTIL: How to Use By and Until Correctly

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What’s the Difference between By and Until in English?

By and Until

How to Use the Word BY

We use by to talk about a deadline when something will happen before that time.

  • By tomorrow
  • By next week
  • By six o’clock
  • By Wednesday
  • By summer
  • By 2020
  • By August…


  • I’ll be back by 11 o’clock.

(The deadline is 11 o’clock so I promise to be back anytime before 11, latest at 10:59)

  • You have to finish by August 31.

(August 31 is the last day you can finish; you may finish before this date.)

  • Will the details be available by December?

(This asks if they will be ready no later than December.)

  • Don’t worry, you will get your books by Thursday.
  • I’d better pay the phone bill. It has to be paid by tomorrow.
  • She is very busy this week. She has to finish this report by Wednesday.
  • They hope to build the offices by March next year.
  • You will need to hand your project in by the end of next week.

How to Use the Word UNTIL

We use until to talk about something that will keep going on for a duration of time from a specific time to another.

  • Until tomorrow
  • Until next week
  • Until six o’clock
  • Until Wednesday
  • Until summer
  • Until 2020
  • Until August…


  • Alan came yesterday. He will stay with us until the weekend.

(Alan is with us at the moment and he is going to stay with us during the time from now to weekend.)

  • They lived in a small house until September 2003.

(They stopped living there in September.)

  • I will be away until Wednesday.

(I will be back on Wednesday.)

  • She is very busy this week. She won’t have any time until Wednesday.
  • Dave will be on holiday until Monday.
  • Yesterday he stayed in bed until 12:00.

We also use until in negative sentences.

For example:

  • Details will not be available until January.

(January is the earliest you can expect to receive the details.)


Sometimes we can use both by and until in a sentence but their meanings differ from one another.

  • He has bad fever. He needs to be in bed until 10 o’clock.

(He is already in bed and he needs to stay in bed.)

  • He has bad fever. He needs to be in bed by 10 o’clock.

(He is not in bed but for his goodness he needs to go to bed latest at 10 o’clock.)

Difference between By and Until | Image

Difference between BY and UNTIL



Monday 10th of June 2019

Thank you very much for the clear visual aids.


Thursday 22nd of March 2018

Is the sentence "by 10 o'clock yesterday night my homework was done and dusted" correct?

Simon Peter

Thursday 22nd of March 2018

It's nice explanation.. easy to use from now

Mohammad Afras

Saturday 2nd of December 2017

I didn't know usage of "BY" before this...

I understand it. Thank you sir..