Menggunakan present perfect, kita bisa menentukan periode waktu sebelum sekarang dengan mempertimbangkan durasinya dengan for + periode waktu atau dengan mempertimbangkan waktu awalnya dengan since + waktu. FOR dan SINCE juga dapat digunakan dengan past perfect. SINCE hanya dapat digunakan dengan perfect tense. FOR juga dapat digunakan dengan simple past.
For + periode waktu
for six years, for a week, for a month, for hours, for two hours
I have worked here for five years.
Since + waktu
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.
Present perfect dengan FOR
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.
Present perfect dengan SINCE
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.