Difference Between By and Until

Prepositions are words that used before a noun. They are used to show direction, time, place or to introduce an object. “By” and “Until” are two prepositions of time that are commonly confused in sentences.

“By” and “Until” are words used so commonly in English and it is important to know the difference between them.

However, “By” is a preposition that functions as a period in a sentence. By indicates a time limit for something to be done or completed.

But the word “Until” means to aim for a specific period of time or before any deadline.

Use Of “By”

“By” refers to the time used to set a time limit for anything that must be completed. This means that the event must end before the deadline. It is used to  highlight a specific moment or moment in the future when that action should be taken or something achieved.

Using “By” using periods.


It is used to indicate a way of doing something.

• She learned to dance by watching videos.

• He saved her from the cliff by holding her hand.

Represents an agent

It is also used to express what causes something.

• This stand is the old man’s rum.

• He drove the bus.

Later than

• My mother is supposed to be here by December.

• Must arrive for dinner by 9 o’clock.

For measurements

• Employee wages increased by 10%

• Share price down by 5%

For unplanned things

• I meet an old friend in the park by luck.

• Sorry, she didn’t know. It happened by mistake.

Use Of “Until”

“Until” is used to describe the state and situation of a period of time at a particular moment. Until and till are standard, but what might surprise you is that “till” is an older word. But the word “till” is used informally instead of to.

We further discuss the usage below:

A specific time or point

• He will help you, but you have to wait until morning.

• He will be in Spain until midnight

Represents distance

• Don’t go there until I get back.

• You cannot meet her until she returns from her trip.

Difference Between By and Until

The preposition “by” is used to express an action that should happen at or before a certain time. Of course, “until” means any situation, action, or condition that changes within a certain period of time.

We use “by” when a specific time is given for something. In contrast, if the focus is not a time limit or before any deadline, then we can use “until” to show that something continues for a given period of time. So “by” is followed by a specific defined time, but this is not the case with “until”.

A simple trick to remember the difference between by and until is that when you have to do something before a certain time and that time is the last time by which the action must be completed, you must use “by”

On the other hand, when something happens up to a certain point in time, i.e. something happens or continues for a certain period of time and then it changes or stops when the point is reached, we use “until”

Comparison Between By And Until

Parameter of ComparisonBYUNTIL
Means“By” means ‘not later’ which indicates something must be  completed.“Until” means ‘how long a situation lasts’.  
Part of speechPrepositions and Adverb.Preposition and conjuction.
UsageUsed to indicate deadline.For period before deadline.
TimeIt is followed by specific time period.No specific time period was observed.


  1. https://academic.oup.com/jos/article-abstract/13/3/221/1673793
  2. https://link.springer.com/article/10.1007/s11673-012-9369-8