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'By the time' introduces a full temporal clause; 'by' is a preposition followed by a noun or time expression.
Side-by-side comparison
"By the time" introduces the deadline before which something will already have happened. It usually goes with the past perfect or future perfect in the main clause.
By the time he arrived, the party had already finished and everyone had gone home.
By the time you finish cooking, the kids will be back from school.
By the time they fixed the leak, the floor was completely soaked.
"By" as a preposition indicates a maximum deadline: the action must be completed before that moment, or right at that moment, not after.
Please send me the report by Thursday so I can review it over the weekend.
The assignment must be handed in by 9 a.m. or it will not be marked.
Can you finish the design by tomorrow morning? The client is waiting.
Common mistake
"By the time she will arrive" is wrong: like "when" or "once", "by the time" is a temporal conjunction that takes simple present when referring to the future. Correct: "By the time she arrives". In past contexts, the main clause takes past perfect: "By the time I arrived, the meeting had already started".
Trick to remember it
- •Does what follows have a subject + verb? It is "by the time" (conjunction).
- •Does it have only a noun or time expression? It is "by" (preposition).
- •"By the time she ARRIVES" vs "by FRIDAY".
Quick rule
"By the time" + present = future (main clause in future perfect). "By the time" + past = main clause in past perfect. "By" + noun = deadline.
Did you know?
The "by the time" construction with future perfect ("By the time you read this, I will have left") is one of the most elegant uses of the future perfect in English, and one of the least frequent in everyday speech. Many native speakers simplify: "By the time you read this, I will be gone." This tendency to simplify compound tenses is a broad trend in modern English, especially American English. The future perfect is far more common in formal written and academic contexts.
Practise what you learned
Exercise 1 · Pick the right one
Please finish the report _____ Friday. The meeting is on Monday.
Exercise 2 · Pick the right one
_____ we arrived, the party was already over.
Exercise 3 · Form the word
Related word pairs
'Before' and 'after' mark temporal sequence; 'while' and 'when' mark simultaneity or connection between two actions.
Present perfect simple indicates a result or completed action; continuous emphasizes duration or an ongoing activity.
'Since' marks the starting point of something active until the present; 'ago' indicates distance into the past from now.
'A' is used before consonant sounds; 'an' is used before vowel sounds.
Bryan López
Founder of SpeakUP Academy