For and Since with the present perfect tense. What's the difference?

For & Since with Present Perfect Tense

We often use for and since with the present perfect tense.

• We use for to talk about a period of time - 5 minutes, 2 weeks, 6 years.
• We use since to talk about a point in past time - 9 o'clock, 1st January, Monday.

for	since
a period of time	a point in past time
	x------------
20 minutes	6.15pm
three days	Monday
6 months	January
4 years	1994
2 centuries	1800
a long time	I left school
ever	the beginning of time
etc	etc

Here are some examples:

• I have been here for 20 minutes.
• I have been here since 9 o'clock.
• John hasn't called for 6 months.
• John hasn't called since February.
• He has worked in New York for a long time.
• He has worked in New York since he left school.

For can be used with all tenses. Since is usually used with perfect tenses only.