The Difference: By & Until/Till (Prepositions)

Using 'By' + Noun

The preposition 'by' means not later than a certain time. In other words, it is used to describe a time limit. Here's an example:

An example of the preposition 'by' with a timeline.

(You will finish it at a time (x) between now and Friday.)

This means that you will do the report no later than Friday. You might do it on Monday, Tuesday, Wednesday, Thursday, or Friday, but no later than this. Friday is the limit or deadline.

I want to go to bed by 10:00 p.m. 

Again, this means that 10:00 p.m. is the latest that you want to go to bed.

Using 'Until / Till'

(Note: until and till have the same meaning. Till is a little more old-fashioned).

The prepositions 'until' and 'till' describe how long an action or situation continues. In other words, it shows when an action or situation ends (stops continuing).

A timeline of the preposition 'until'

This means the action of sleeping (the red line) continued all night until the morning, at 10:00 a.m., when you woke up. This is when your sleeping ended.

My father will be away until next month.

Again, this means the situation of your father being away will continue until next month. He will come home next month, and then he won't be away.

Hint: Sentences with 'until' often also have the preposition 'from', for example:

  • My father will be away from today until next month.
  • I slept from 10 p.m. until 10 a.m.



  • The preposition by describes a limit for when an action should be done.
  • The proposition until shows when a (continuing) action or situation ends.

Example: A Carton of Milk

an old carton of milk

Here is a carton of milk. You bought it on December 1st, and it is still fresh. On the carton, what would it say?

    1. Please drink on December 20th.
    2. Please drink by December 20th.
    3. Please drink until December 20th.
Show Answer

1. Please drink on December 20th.

Incorrect: Why would you have to wait twenty days to drink it?

✔ 2. Please drink by December 20th.

Correct: This means that the milk should be drunk no later than December 20th. After this, it is not fresh anymore. In other words, December 20th is the last day (the time limit) for drinking the milk.

3. Please drink until December 20th. 

Incorrect: This means the action (drinking) should continue until December 20th. That means drinking continuously for twenty days! The act of drinking only takes a few seconds. It is (almost) impossible to drink or eat something until another day because that means you would be eating or drinking for more than 24 hours.

Common Mistake: Using 'Until' with Short Actions

I started reading until 10 o'clock at night.

I read until 10 o'clock at night.

We do not use 'until' with short actions (e.g. start/stop, became, notice, recognize, fall asleep, wake up) because these verbs do not continue long enough to use until. How long does it take to start something? When you started reading this webpage, it took you one second. Starting does not take time (but reading does!). Similarly, although it may take time to get out of bed, waking up takes a few seconds. We don't use until with verbs that cannot have a long length.


Do you think you understand the difference between by and until? Try our exercises below.

Exercises 1: By and Until

  1. The game was on TV from 7  9 p.m.
  2. Ken has to be home  6 o'clock tonight because his mother is preparing a special dinner.
  3. Please wait  I'm finished.
  4. Alan lent his computer to his friend and told him to give it back  the end of the day.
  5. Paul and Christina try to get their baby to fall asleep  7:30, but they don't always succeed.



Exercises 2: By and Until

  1. The turkey will take four hours to cook. We want to eat around six o'clock, so the turkey has to be in the oven  two p.m.
  2. The turkey will take four hours to cook. We want to eat around six o'clock, so the turkey will be in the oven from two  six o'clock.
  3. Please let me know  Saturday if you can come to the party.
  4. Francesca was offered a job today. She told the company that she would make a decision  Thursday.
  5. The power company said they'd shut off my power if I don't pay my bill  Friday at noon.


Exercises 3: By and Until

John woke up at 7:30 a.m. He showered, got dressed, and ate breakfast from 7:30 to 8:20. Then he left his house to walk to college. He arrived five minutes before class started, at 8:55.

Base on the above story, we can make the following sentences:

  1. John slept  7:30 a.m.
  2. He got ready (showered, dressed, ate) from 7:35  8:20.
  3. He arrived at college  9:00 a.m.
  4. He will study hard  he graduates.
  5. He hopes to start his own company  the age of 30, but he knows that this won't be easy.


Bonus: Are 'Until' and 'Before' the same?

Not exactly. 'Until' describes when a continuous action ends. 'Before' just means the action happened before another (it may not have continued up to that time). Compare:

  • The boy studied until he fell asleep. (We know the action of studying continued until his eyes closed.)
  • The boy studied before he fell asleep. (The boy may have done other things after studying, such as brushing his teeth, reading a book, etc.)

By & By the time: Grammar Difference

'By' is used with a noun phrase, e.g. by 2030, by Friday, by six o'clock.

'By the time' can be used with a clause that contains a subject and a verb. For example:

By the time dad returns home, we need to clean up the house.

Gloria wants to start her own company by the time she is 30.

In short, if you want to use a noun (e.g. a time, day, month, or year), use 'by'. If you want to use a full sentence, use 'by the time'.

Note: By the time has another meaning as well, which is not described here.

I hope this page has been useful. If you have a comment, please leave it below.

-- Written by Matthew Barton (copyright), creator of

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6 comments on “The Difference: By & Until/Till (Prepositions)

  1. BLADIMIR RODRIGUES. (Posted on 5-30-2021 at 18:07) Reply

    I like to practice

  2. Ayjeren (Posted on 6-13-2021 at 12:33) Reply

    It was great and understandible

  3. Anonymous (Posted on 7-25-2021 at 02:52) Reply

    The perfect explanation ever. Thank you :)

  4. Ha Kiki (Posted on 2-6-2022 at 05:08) Reply

    So useful

  5. Bahara (Posted on 2-12-2022 at 06:45) Reply

    It was so helpful thanks

  6. Gurbangeldi (Posted on 6-4-2022 at 02:13) Reply

    It was great.I understood everything. Thanks

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