Grammar guide Updated 2026-10-06
Since, For and Ago: Time Markers for the Present Perfect
Three short words carry most of the time information in present perfect and past simple sentences. For measures a period, since names a starting point, and ago counts backwards from now to a finished moment.
The rule in one line
| Marker | Followed by | Example |
|---|---|---|
| for | a length of time | I have lived here for five years. |
| since | a starting point | I have lived here since 2021. |
| ago | a point counted back from now, with the past simple | I moved here five years ago. |
The question to teach: a period, a starting point, or a finished moment?
1. For plus a period of time
For is followed by a length: for three years, for ten minutes, for ages. It answers How long? and is not tied to one tense. I lived there for three years is finished. I have lived there for three years reaches the present. I'm staying with my sister for a week looks forward.
2. Since plus a starting point
Since marks where something began: since 2020, since Monday, since I was a child. It takes a noun or a clause. A since clause takes the past simple while the main clause takes the present perfect: I have known her since we were at school. Since I left school I have worked in three cities.
3. Where the two markers sit
Both usually go at the end: I have worked here for six years. I have worked here since 2020. For six years I have worked here is also possible.
4. Ago belongs to the past simple
Ago counts back from now and always pairs with the past simple: I moved here two years ago. It cannot appear with the present perfect, so I have moved here two years ago fails. Change the marker instead of the tense: I have lived here for two years. Note also that before points back from a past moment, not from now.
5. Since and ago point in opposite directions
Since 2020 starts in 2020 and comes forward to now, so the period is open and the tense is present perfect. In 2020 or two years ago sits at a finished point, so the tense is past simple. Compare I have been a teacher since 2018 with I became a teacher in 2018.
6. Traps worth naming
One situation can need two structures: I have been here for two years and I came here two years ago. It has been three years since I visited Rome again takes the past simple after since. And I haven't seen him for ages is more natural than since ages, because ages is a length.
7. Question forms
How long have you…? asks about a period reaching the present, so the answer carries for or since: For about ten years. Since 2016. When did you…? asks about a finished moment, so the answer carries ago or a past date: Three years ago.
8. Twelve contrast pairs
- I have lived here for five years. / I moved here five years ago.
- She has worked there since 2019. / She started there in 2019.
- We have been married for twelve years. / We got married twelve years ago.
- I haven't eaten since breakfast. / I ate breakfast at seven.
- It has been raining for three hours. / It started raining three hours ago.
- He has had that car for ages. / He bought that car ages ago.
- I have known her since we were children. / I met her as a child.
- How long have you had that coat? / When did you buy that coat?
- I have worked here for six months. / I joined the company six months ago.
- They have lived abroad since 2015. / They went abroad in 2015.
- I haven't seen him for two weeks. / I last saw him two weeks ago.
- She has been off work since Monday. / She went off work on Monday.
Six sentences to correct
- I have seen him two days ago. I saw him two days ago.
- She has worked here since three years. She has worked here for three years.
- We are friends for ten years. We have been friends for ten years.
- It has been three years since I have visited Rome. It has been three years since I visited Rome.
- I live here since 2020. I have lived here since 2020.
- How long do you know her? How long have you known her?
The have gone to / have been to pair is a related error: He has gone to Paris means he is still there, while He has been to Paris means the visit is over. The present perfect continuous guide carries the wider picture.
9. Four classroom drills
Drill 1: timeline sort. Give pairs cards such as "since 2019", "for three weeks" and "two days ago", plus three labelled columns. They sort the cards and write a sentence for each.
Drill 2: correction relay. Post the six sentences around the room. Pairs rewrite each one and defend the change.
Drill 3: How long mingle. Students interview three classmates with How long have you…? questions and report back with for and since: Marta has played the piano since she was six.
Drill 4: three personal sentences. Each student writes three true sentences, using for, since and ago once each.
Printable. The gap sentences and correction list join the classroom grammar drills collection. The past perfect guide is the natural follow-on.
10. Four errors to correct early
- For with a point. for 2020 should be since 2020.
- Since with a period. since three years should be for three years.
- Ago with the present perfect. I have seen him two days ago should be I saw him two days ago.
- A perfect since clause. since I have left school should be since I left school.
Frequently asked questions
What is the difference between for and since?
For goes with a length of time, as in for three years; since goes with a starting point, as in since 2019. Count the period and use for; name the moment and use since.
Why is I have seen him two days ago wrong?
Because ago looks back from now to a finished moment, which the past simple describes. Say I saw him two days ago.
Which tense follows since in a clause?
The since clause takes the past simple, the main clause the present perfect: I have known her since we were at school.
Where do since and for go?
Both usually sit at the end: I have worked here for six years; since 2020, I have worked here.
How long have you or When did you?
How long have you asks about a period reaching the present, so the answer uses for or since. When did you asks about a finished moment, so the answer uses ago.