By or Until

Until talks about a continuing action that finishes at a point in the future.
By talks about the finish of an action at a point in the future.

  • I’m staying in the city until June.
    (continuing action/staying in the city)
  • I will keep working until I have finished.
  • I will finish my journey by Friday.
    (finish of an action/journey)
  • Please have it finished by tomorrow.