When do you use "by" instead of "until"?

If you speak German, there's a good chance you've written something like "I'll send it until Friday." It makes sense, because German uses bis for both. English splits that job between two words, "by" and "until," and once you see what each one does, choosing gets much easier.

By

"By" is all about deadlines. It means "no later than." The action happens once, at any point up to that time.

• Be home by 10 p.m.
• Can you finish the presentation by Monday?
• Please send your application by the end of the week.
• I'll have the report ready by your morning coffee.

It doesn't matter exactly when it happens, as long as it's not later. If you finish the presentation on Saturday, great. If it's done on Tuesday, you've missed the deadline. 

Until

"Until" is about how long something keeps going. The action continues the whole time, then stops at that point.

• Wait here until I get back.
• The shop is open until 9 p.m.
• She read until she fell asleep.
• The party went on until midnight.
• Bake the cake until it's golden brown.

In conversation, you'll often hear "till" instead, as in "I'm at work till six." It means the same thing.

You'll also see "not until," which means something won't happen before a certain time:

• The package won't arrive until Thursday.
• I don't start work until ten tomorrow.

If you're not sure which one you need, ask yourself whether the action happens once or keeps going. "Finish it by Friday" means it gets done at some point before Friday. "Work on it until Friday" means you keep working the whole time, then stop.

For a more interactive learning experience, check out our Daily Dose of Denglisch Docs series.