Present perfect continuous

An action that began in the past and continues up to the present.

I've been working for this company since 2002.

An action which started in the past and lasted for some time. The result of the cation is visible in the present.

David's been playing tennis so he's really tired.

I have been going to the gym for a moth. I've lost 20 pounds.

We use the Present perfect continuous to emphasise the duration of an action which started in the past. For finished actions we use the present perfect simple.

We have been living in London for twelve years. (We still live there now)

They've lived in Moscow, Berlin and Madrid. (They don't necessarily live there any longer)

"How long" is the most common time expression used with the present perfect continuous. "How often/How many/How much" is usually used with the present perfect simple.

How long has she been sleeping?

How often have you worn that suit?

How many English lessons have you had?

When we use verbs describing an state or situation (e.g. have, like, love, know), we don't use the continuous form.

I've had an iPod for two years.

I've been knowing you for a long time. (Incorrect)

I have known you for a long time. (Correct)