for vs. since
Two of the most commonly confused prepositions in English — both used with the present perfect, but for very different purposes.
The mistake
I have lived here since three years.
I have lived here for three years.
She has been waiting for 9 o'clock.
She has been waiting since 9 o'clock.
The rule
The key difference is simple: for describes a length of time (a duration), while since marks a specific point in time when something began.
| Word | Describes | Followed by | Examples |
|---|---|---|---|
| for | A duration — how long | A period of time | for two hours, for a week, for years |
| since | A start point — when it began | A point in time | since Monday, since 2019, since breakfast |
Using for
Use for when you say how long something has lasted. The time expression that follows is always a period or duration.
I have studied English for five years.
We waited for a long time.
She has worked here for six months.
Using since
Use since when you name the moment something started — a clock time, a date, an event, or a noun that pins a point in time.
I have studied English since 2019.
We have lived here since January.
He hasn't called since the argument.
A quick test
Ask yourself: Am I saying how long, or when it started?
- How long? → use for → for three days
- When did it start? → use since → since Tuesday
Tip: Both for and since are used with the present perfect and past perfect, but for can also appear in simple tenses: I lived there for a year (past simple). Since, however, almost always requires a perfect tense.