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:

(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).

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.

Example: A 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. 1. Please drink on December 20th.
   2. Please drink by December 20th.
   3. Please drink until December 20th.

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

Exercises 2: By and Until

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.

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 Englishcurrent.com

Related Page

• Preposition Exercises