We often use for and since with the present perfect to talk about something continuing up to the present.
FOR + a period
A period is a duration of time, for example: 5 minutes, 2 weeks, 6 years.
For means "from the beginning of the period until the end of the period."
For can be used with all tenses.
SINCE + a point
A point is a precise moment in time, for example: 9 o'clock, January 1st, Monday, my birthday.
Since means "from a point in the past until now."
Since is normally used with perfect tenses.
In the table below you'll find a summary:
|A PERIOD (From Start To End)||A POINT (Up To Now)|
|ALL TENSES||PERFECT TENSES|
|20 minutes, three days, 6 months, 4 years, 2 centuries, a long time, ever, etc||9am, Monday, March, 1998, 1666, I left school, the beginning of the year, etc|
After reading this lesson you may want to do some exercises, then click HERE.