Part 10: By vs Until - English In A Minute

If I say: I have to take care of my dog until 5pm, it means I will start taking care of my dog now and stop taking care of it at 5pm.

On the other hand, we use 'by' to talk about doing something before a future time or deadline.

If I say: I have to finish an essay by 5pm, it means I can start any time

but I will make sure that at 5pm I have finished writing the essay.

So, I may even finish it at 3pm or any time before 5.

So we use 'until' to describe doing something up to a certain point in time

and we use 'by' to describe doing something before a future time or deadline.