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What’s the difference between by and until?

By and until are not interchangeable in English. Although their meaning is similar, we use them differently.

By means no later than, and introduces a deadline, whereas until gives information about the point when an action or time period ends.

Take a look at the examples below to find out more about when to use by and when to use until in English, then test out your knowledge in the free exercises.


Tomorrow is the final exam.

You have until the end of class today to revise grammar and vocabulary.

You must be here by 8:15 tomorrow morning.

The exam starts at 8:30 and you have until 11 to answer all of the questions.


By is a preposition of time, it shows that an action will be completed before or at a certain time point. We use by with specific times or dates to indicate a deadline, as well as in the expression by the time. By often implies a sense of time pressure, and therefore usually appears together with modal verbs of obligation such as have to and must.

  • by + time/date/day = no later than
You must be here by 8:15 tomorrow.


Until and till have the same meaning. Until is more formal than till (’til is the American spelling).

  • until shows us the point where an action stops; it indicates the end of a block of time
You have until the end of class to revise for the exam.
At the end of class the students will stop revising.
  • use until, till and to as a preposition of time in the expression from … to/till/until
The exam goes from 8:30 to/until/till 11 tomorrow.


By or until can greatly affect the meaning of a sentence.

I’ll be home until 7pm.

I am at home now, but I won’t be here after 7pm.

I’ll be home by 7pm.

I am not at home now, but I will be home no later than 7pm.