Finish by vs. finish until

WRONG: I have to finish the project until Friday.
RIGHT: I have to finish the project by Friday.

This week’s Czenglish error is a small but significant one that takes a bit of explaining. It concerns the use of ‘by’ and ‘until’ in terms of a deadline.

You cannot say, „I have to finish the project until Friday.“ The word order is wrong, making the sentence sound strange. In English, you have until a time to do something, you don’t finish something until a time. So here, you have to say, „I have until Friday to finish the project.“

The alternative way of saying this information is – „I have to finish the project by Friday.“ Friday is the deadline you have to do something by. The word ‘by’ comes at the end of the sentence followed by the time clause.

So is there any difference between the two correct sentences? Yes, slightly. When you use ‘until‘ you are stressing the days before the deadline. For example, you are saying, „I have until Friday, that’s plenty of time!“ When you use ‘by’ you are stressing the deadline, meaning „Oh no, I have to work quickly, the deadline is on Friday!“

So together:

Boss: You have to finish the project by Friday.

Employee: By Friday? I’ll never manage it. Can you give me until Monday to do it?

Boss: Ok, you have to finish the project by Monday, at the very latest!