By and until both look at a moment in the future, but they mean opposite things about time before it. By says "at or before this moment". Until says "continuously up to this moment".
The verb tells you which one fits. A completed action with a deadline takes by: finish the report by Friday. A continuing state or activity takes until: stay at work until Friday. If the situation stops at the moment, use until.
This page shows the deadline test, the negative patterns, and by the time. Then a 20-question drill checks every pattern with an explanation under each answer.
The rule
By: the deadline
- By means not later than: "Send the invoice by Monday." Monday is the last acceptable moment.
- By works with a finished action: finish, send, return, pay, decide, arrive.
- By is common with the future perfect: "By Friday, I will have finished the report."
- By the time adds a clause: "By the time we arrived, the film had started."
Until: the end of a period
- Until means up to a point in time and then the situation changes or stops: "The shop is open until nine."
- Until works with continuing states and activities: wait, stay, sleep, work, be open, keep going.
- Not until marks the moment something starts: "I did not sleep until midnight."
- Till is a less formal way to write until, and both have the same meaning.
The verb test
- Ask whether the verb describes a moment or a stretch of time.
- A moment of completion takes by: "I will pay by Friday."
- A stretch that continues takes until: "I will keep the money until Friday."
- If both seem possible, the sentence meaning changes: by Friday means the payment is done; until Friday means the money stays with you.
By, until and negatives
- Not until means "only at that moment": "She did not arrive until ten."
- Not by does not form this pattern. Use not until or not before.
- By now means "already, or expected before this moment": "They should be here by now."
- Until now describes a period that has just ended: "Until now, I never understood the rule."
From, to and other pairs
- From and until show a range with a clear end: "The course runs from March until June."
- From and to do the same job, and to sounds more natural with timetables: "from nine to five".
- By can also mean "beside" or "by means of", but the deadline meaning is the one that contrasts with until.
- In negative sentences about waiting or starting, until is almost always the right choice.
Examples
- Please submit the essay by Thursday.The essay is finished at or before Thursday, so by is correct.
- The library stays open until ten.The open state continues up to ten, so until is correct.
- I will have cooked dinner by the time they arrive.By the time marks a deadline before another event.
- We waited until the rain stopped.Waiting continues up to the moment the rain stops.
- She had left by six o'clock.Her leaving was complete before six, a deadline sense.
- He did not get home until very late.Not until marks the moment the action finally happened.
- I will keep your seat until the show begins.Keeping the seat is a continuing action, so until fits.
- Can you finish the task by tomorrow morning?The task ends at the deadline, so by is needed.
- They should have arrived by now.By now expects finished arrival at or before this moment.
- Until last year, she had never travelled abroad.Until last year describes the period before the change.
Common mistakes
- Wrong: I will wait by six o'clock. Right: I will wait until six o'clock.
- Waiting is a continuing action, so it takes until. By would mean the waiting is complete at six.
- Wrong: Please finish the report until Friday. Right: Please finish the report by Friday.
- Finish is a completed action with a deadline, so by is correct.
- Wrong: She was working by midnight. Right: She was working until midnight.
- The work continued up to midnight, so until fits the stretch of time.
- Wrong: I did not sleep by ten. Right: I did not sleep until ten.
- Not until marks the moment the action started. Not by is not used in this pattern.
- Wrong: By now, I have waited two hours. Right: Until now, I have waited two hours.
- The waiting period continues up to the present moment, so until now describes it.
Practice drill
Answer all 20 questions. Each answer is marked at once, and the rule is explained under the question.
Please send the money ___ Monday at the latest.
Show answer and explanation
Answer: A. by By sets a deadline: the money is sent not later than Monday.
The pool is open ___ nine every evening.
Show answer and explanation
Answer: B. until The open state continues up to nine, so until fits the period.
I will finish the book ___ Friday.
Show answer and explanation
Answer: C. by Finishing is a completed action with a deadline, so by is correct.
We waited ___ the bus arrived.
Show answer and explanation
Answer: D. until Waiting continues up to the moment the bus arrives, so until fits.
She had already left ___ the time I called.
Show answer and explanation
Answer: A. by By the time marks a deadline before another past event.
He did not wake up ___ noon.
Show answer and explanation
Answer: B. until Not until marks the moment the action finally started.
I will keep the ticket ___ the end of the month.
Show answer and explanation
Answer: C. until Keeping the ticket is a continuing state, so it takes until.
Can you be home ___ six?
Show answer and explanation
Answer: D. by Being home at a latest moment is a deadline, so by is needed.
They should have called ___ now.
Show answer and explanation
Answer: A. by By now expects a completed action at or before this moment.
___ last summer, I had never seen the sea.
Show answer and explanation
Answer: B. Until Until last summer describes the period before the change happened.
The course runs from April ___ July.
Show answer and explanation
Answer: C. until From and until show the range of a continuing course.
I will have packed my bags ___ the taxi arrives.
Show answer and explanation
Answer: D. by By the time sets a deadline before the taxi arrives.
He stayed at his desk ___ midnight.
Show answer and explanation
Answer: A. until Staying is a continuing action, so it takes until.
Please decide ___ tomorrow morning.
Show answer and explanation
Answer: B. by Deciding is a completed action with a deadline, so by is correct.
She worked at the cafe ___ she finished university.
Show answer and explanation
Answer: C. until The work continued up to the moment she finished, so until fits.
We did not leave the house ___ the rain stopped.
Show answer and explanation
Answer: D. until Not until marks the moment the leaving happened.
Apply ___ 30 June and start in September.
Show answer and explanation
Answer: A. by The application deadline means the action happens not later than 30 June.
The shop stays busy ___ late every Friday.
Show answer and explanation
Answer: B. until Staying busy is a continuing state, so until describes the period.
Have you finished the exercise ___ now?
Show answer and explanation
Answer: C. by By now asks whether the action is complete at this moment.
I knew nothing about the plan ___ yesterday.
Show answer and explanation
Answer: D. until Until yesterday describes the period before the news arrived.
Drill complete
You answered every question.
Next topic: How much vs how many: count the nounTake the level test
Questions learners ask
Is "till" different from "until"?
No. Till is a shorter, more informal form of until, and both mean up to that point. In careful writing, until looks better at the start of a sentence: "Until we hear from them, we cannot decide."
Can I use "by" with a state verb?
By focuses on the moment of completion, so it pairs with actions and achievements: be home by nine, know the answer by Friday. A continuing state such as stay, sleep or be open normally takes until. The question is whether the sentence is about the end of a stretch.
What does "by the time" mean?
By the time introduces a clause that sets a deadline: "By the time you read this, I will have left." It often appears with the past perfect or the future perfect because one action finishes before the other.
More grammar topics
How much vs how many: count the noun
How many counts separate things. How much measures an amount, a price or an uncountable idea.
Ever and never with the present perfect
Ever means at any time up to now, and it lives in questions. Never means at no time up to now, and it lives in statements.
Zero conditional: facts and habits
When the result is always true, both halves of the sentence take the present simple. If and when mean the same thing here.
Take the free A1 to C2 level test to find your starting point.