I will have left by the time you arrive.

I will have left when you arrive.

I will have left before you arrive.

Do the three sentences mean the same thing? Could native speakers please explain them for me if they are not the same? Also, please tell me when I must use “by the time.” Thank you.

  • 1
    They all mean exactly the same, because you set the "temporal context" with initial I will have left... But if we were contrasting I left when / before you arrived they would mean different things. And many people wouldn't accept I left by the time you arrived as valid anyway (we'd expect I had left... there). Commented Jul 23, 2023 at 13:15

1 Answer 1


All these sentences describe the same sequence of events: I leave, then you arrive.

I can't think of any nuance meaning differences either, nor any contexts where one would be clearly preferred over the others.

The first is the most natural because English speakers like using "by" time expressions with perfect tenses.

  • 3
    I definitely agree that they have the same meaning and that the first is the best sounding. I would personally never use the second of the three though, because "when" seems to imply "exactly the same time as," while "will have left" seems to imply "before," so it sounds inconsistent Commented Jul 23, 2023 at 4:33
  • 2
    @QuackE.Duck Agreed. I don't think I'd ever use the second. It's not bad grammar or marked, but the other phrases are just significantly more natural in any context I can think of.
    – gotube
    Commented Jul 23, 2023 at 5:10
  • 2
    The third also sounds unnatural. Most would say "I will leave before you arrive."
    – Barmar
    Commented Jul 23, 2023 at 13:52

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