For and Since are the two so-called markers of the Perfect tenses (Present /Past Perfect, Present/Past Perfect Continuous), which means that they usually go together. The difference between these two words is quite big, yet many English learners often confuse them.
We use for + a complete period of time (e.g. four days, three years etc.)
- I have been there for three days.
- We have been waiting for five hours.
- They have been gone for a month.
We use since + the starting point of the period (e.g. their childhood, 1993 etc.)
- I have been learning Spanish since I was eight years old.
- He has worked at a bank since 2012.
- His daughter has been going to school since September.
Check yourself by completing the sentences with FOR or SINCE:
- Marilyn has been in Madrid ……. three days.
- Ruth has lived in Madrid ……. she was nine years old.
- I have known Jerry …… 2001.
- We have been talking ……. two hours!
- They have been married ……. six years.