The Use of By & Until

The Use of By & Until : Grammar & Spelling Tips

When do we use BY?

We use by to set a time limit for completion:

• It must be ready by Friday.
• It can be ready before Friday, but Friday is the final day. (By is a preposition here.)

When do we use UNTIL?

We use until when the activity continues throughout the period up to the time limit:

• I'll be here until five o'clock.
• Between now and five o'clock, I shall be here all the time. (Until can be a preposition (until five o'clock) or a conjunction (until you have finished.) )