Grammar › Prepositions › By vs Until
By vs Until
Both point to a future time, but they work differently:
- by — a deadline for a single action (Send it by Monday = on or before Monday).
- until / till — a state that continues up to a point (Stay until Monday = the whole time up to then).
Use 'by' with finish/send/arrive (one action); use 'until' with wait/stay/keep (a continuous situation).
by vs until
| Word | Meaning | Verb type | Example |
|---|---|---|---|
| by | on or before (deadline) | single action | Finish it by Friday. |
| until / till | continuously up to | continuous state | Wait until Friday. |
| by the time | when + clause | — | By the time we arrived, it had ended. |
When to use each
1. by — a deadline
- Please reply by tomorrow. The train arrives by 9.
2. until — a continuous situation
- The shop is open until 8. I’ll wait here until you’re ready.
3. by the time — with a clause
- By the time the film started, we’d eaten all the popcorn.
⚠️ Compare: I’ll finish by 6 (one action, at or before 6) vs I’ll work until 6 (continuous, stopping at 6).
Common mistakes
1. ‘until’ for a deadline. Finish it until Friday → Finish it by Friday.
2. ‘by’ for a continuous situation. I’ll wait by 6 → I’ll wait until 6.
3. ‘by’ + a clause. By we arrived, it had ended → By the time we arrived, it had ended. Pro tip: by = deadline (single action); until = keep doing it up to a point.
✏️ Practice: By vs Until
1. Please send the report ___ Friday.
2. The shop stays open ___ 9 p.m.
3. I'll wait here ___ you get back.
4. We need to leave ___ 8 or we'll miss the train.
5. ___ we arrived, the party had already finished.
6. He worked at the company ___ 2020, then moved abroad.
7. Can you finish this ___ the end of the day?
8. Correct this: 'I'll wait by you're ready.'
9. Correct this: 'Pay the invoice until the 15th.'
10. Which word means 'continuously up to a point'?
Frequently asked questions
What's the difference between by and until?
'By' is a deadline for a single action (Reply by 5 = at or before 5). 'Until' is a period that continues up to a point (Wait until 5 = keep waiting until then).
Which verbs go with each?
'By' with one-off actions (finish, send, arrive, pay by Friday). 'Until' with continuous states (wait, stay, work, sleep until noon).
By or by the time?
'By' + a time (by 6). 'By the time' + a clause (By the time I got home, dinner was ready).
Is 'till' the same as 'until'?
Yes. 'Till' is a slightly more informal spelling of 'until'; both are correct.
👩🏫 For teachers
CEFR objectives for “By vs Until”:
- Can use 'by' for a deadline (single action, on or before) (CEFR B1).
- Can use 'until/till' for a continuous situation up to a point.
- Can use 'by the time' + a clause.
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