Since vs For: A Starting Point or a Length of Time?
Choose since or for with clear time expressions, present-perfect examples, finished past situations and a simple way to avoid since two years.
The useful difference is small: since names a starting point; for gives a length of time. Think since Tuesday and for three days. I'd choose the time expression first, then check whether the verb fits the situation you mean.
Point to the start, or measure the stretch
Since September, since lunchtime and since I moved all locate a beginning. For a month, for half an hour and for ages describe duration. That is why since two years does not work for a two-year period: say for two years.
Imagine a neighbour who still lives in the same flat. She has lived here since 2022 gives the starting year. She has lived here for four years gives the length of time at a suitable point in 2026. Both descriptions can refer to the same situation.
When the situation is still true
Use the present perfect for many states that began earlier and continue now: I have known Amina for six months or We have had this table since March. The pattern is have or has + past participle. Avoid I know her since March when you mean that the relationship began then and continues now.
A starting point can be a whole clause: We have been neighbours since she moved in. The move is a completed event; the relationship continues. You do not have to put every verb after since into the present perfect.
For does not choose your tense
We waited for forty minutes describes a finished wait. We are staying for two nights describes an arranged visit. The office will close for a week describes a future closure. For marks duration in all three; the verb tells you when the situation happens.
My practical suggestion is to keep the full meaning together: still true now, finished or planned. Then pick the verb and the time phrase. The word for alone is not a signal to use the present perfect.
Keep exploring
Present perfect vs past simple · Present perfect simple vs continuous
Sources and editorial notes
Sources checked on 19 October 2026. Cambridge's official indexed explanation supports the point/duration distinction and for with past, present or future reference; direct retrieval returned 403. Oxford's grammar page was read directly for present-perfect patterns and since clauses. All examples and the neighbour scenario are original. Since also has other uses, including giving a reason; this post focuses on time.
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