For and Since for Time
We often use for and since when talking about time.
for + 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 + point
A point is a precise moment in time, for example: 9 o'clock, 1st January, Monday. Since means "from a point in the past until now." Since is normally used with perfect tenses.
for
a period
(from start to end)
>===< 
since
a point
(up to now)
x===> 
for 20 minutes
for three days
for 6 months
for 4 years
for 2 centuries
for a long time
for ever
etc 
since 9am
since Monday
since January
since 1997
since 1500
since I left school
since the beginning of time
etc 
all tenses 
perfect tenses only 
For can be used with all tenses. Here are a few examples:
 They study for two hours every day.
 They are studying for three hours today.
 He has lived in Bangkok for a long time.
 He has been living in Paris for three months.
 I worked at that bank for five years.
 Will the universe continue for ever?
For is NOT used with "all day", "all the time" etc.
 I was there all day. (not *for all day)
Since is normally used with perfect tenses:
 He has been here since 9am.
 He has been working since he arrived.
 I had lived in New York since my childhood.
Since can also be used in the structure "It is [period] since...":
 It is a year since I saw her.
 How long is it since you got married?
Now check your understanding »
Both for and since also have other meanings, with no reference to time. Here are some examples:
 This is for you.
 Is this the train for London?
 Since you ask, I'll say yes.
 Since he didn't study he didn't pass the exam.
