Form and rules
How it works
1
Use the present perfect simple for completed results and quantities: I've written three emails.
2
Use the present perfect continuous for duration or an activity continuing until now: I've been writing for two hours.
3
How many/how much often points to the simple form; how long often points to the continuous, but meaning is more important than the question word alone.
4
State verbs such as know, own and believe normally use the simple perfect, not the continuous.
5
With verbs such as live, work and study, both forms can be possible; the continuous usually puts more focus on activity, duration or temporary effort.