現在完了形を使う場合、for + 期間を使ってその期間,を考慮したり、since + 時点を使ってそれが始まった時を考慮することができます。 FORとSINCE は、過去完了形でも使うことが出来ます。SINCE は完了形のみで使え、FOR は単純過去形でも使えます。
For + 期間
for six years, for a week, for a month, for hours, for two hours
I have worked here for five years.
since this morning, since last week, since yesterday
since I was a child, since Wednesday, since 2 o'clock
I have worked here since 1990.
She has lived here for twenty years.
We have taught at this school for a long time.
Alice has been married forthree months.
They have been at the hotel for a week.
She has lived here since 1980.
We have taught at this school since 1965.
Alice has been married since March 2nd.
They have been at the hotel since last Tuesday.