More Time Prepositions (for, since, during, by, until...)

Intermediate · Prepositions

Beyond in/on/at, several other prepositions handle durations, deadlines, and starting points. These are where a lot of subtle errors happen — especially "for" vs "since", "by" vs "until", and "during" vs "for".

Learn each as a clear contrast and the confusion disappears.

How to build it

for + period · since + start point · during + event/noun · by = deadline · until = up to that time · in = after (future)

Rules & examples

1. "for" + a length of time; "since" + a starting point.

   for answers "how long?"; since answers "starting when?"

   • for three years, for two hours
   • since 2010, since Monday
2. "during" + a noun/event (when something happens); "for" + how long.

   during tells you WHEN (inside what event); for tells you the DURATION.

   • I slept during the film.
   • I slept for two hours.
3. "by" = not later than a deadline; "until/till" = up to that point in time.

   by = a single deadline moment; until = a continuous action stops then.

   • Finish it by Friday. (deadline)
   • I'll wait until Friday. (the whole time up to then)
4. "in" can mean "after" a period in the future.

   A future time from now.

   • I'll be there in ten minutes.
   • The train leaves in an hour.
5. "from ... to/till/until" for a start and end; "ago" for past distance.

   ago goes AFTER the time and means "before now".

   • open from 9 to 5
   • two years ago
   • a moment ago

Tips to remember

• "by" vs "until": you DO something BY a deadline (one action), but you WAIT/keep doing something UNTIL a time (continuous).
• "ago" comes after the time and works with the past simple: "I met him three days ago."

Common mistakes

• ✗ I have lived here since five years. → ✓ I have lived here for five years. — "for" + a length of time; "since" + a start point (since 2019).
• ✗ I must finish until Monday. → ✓ I must finish by Monday. — A deadline uses "by"; "until" is for something continuing up to a time.