PRESENT PERFECT TENSES

Present Perfect Simple – Present Perfect Continuous

Both tenses are used to express that an action began in the past and is still going on or has just finished.
Before we go on, remember that some verbs are NOT used in the continuous tenses, whether it's the present perfect continuous or any other:

Certain verbs are not used in continuous tenses

The following verbs are usually only used in Present Perfect Simple (not in the continuous form).

• state: be, have (for possession only): We have been on holiday for two weeks.
• senses: feel, hear, see, smell, taste, touch: He has touched the painting.
• brain work: believe, know, think, understand: I have known him for 3 years.

 (It's a bit more complicated than this, but we can't go into details now)

 
 In many cases, both forms are correct, but there is often a difference in meaning: We use the Present Perfect Simple mainly to express that an action is completed or to emphasise the result. We use the Present Perfect Continuous to emphasise the duration or continuous course of an action.

Result or duration?

Do you want to express what has happened so far or how long an action has been going on yet?

Present Perfect Simple	Present Perfect Continuous
Result (what / how much / how often)	Duration (how long)
I have written five letters/ I’ve been to London twice	I’ve been writing for an hour

Emphasis on completion or duration?

Do you want to emphasise the completion of an action or its continuous course (how has somebody spent his time)?

Present Perfect Simple	Present Perfect Continuous
Emphasis on completion	Emphasis on duration
I have done my homework. (Meaning: My homework is completed now.)	I have been doing my homework. (Meaning: That's how I have spent my time. It does not matter whether the homework is completed now. Probably not)

Result or present results?

Do you want to express that a completed action led to a desired result or that the action had an unwanted side effect?

Present Perfect Simple	Present Perfect Continuous
desired result	action has just stopped but has present results ("side effect")
I have washed the car. (Result: The car is clean now.)	Why are you so wet? - I have been washing the car. (side effect: I became wet when I was washing the car. It does not matter whether the car is clean now.)

 Signal words

Present Perfect Simple	Present Perfect Continuous
how many times …times	how long  (But remember that some verbs since         can't be used in the continuous!)  for

And now, let’s be practical…

• ·         When we ask or say HOW LONG, the continuous is more usual. This is very common with verbs like LIVE, WORK, RAIN, LEARN, WAIT, DO STUDY, etc.:

I’ve been learning English for six months.

It’s been raining since lunchtime.

Richard has been doing the same job for twenty years.

How long have you been driving?              --Since I was 18.

I’ve been cooking all morning.

This use often translates as LLEVA + gerundio: lleva nevando, llevo trabajando, hace
 cuánto que + presente

• ·         Use the continuous when talking about “present results”:

My hands are cold because I’ve been doing the washing-up with cold water.

His clothes are greasy because he’s been cooking.

He’s sweating because he’s been working out in the gym.

• ·         When the emphasis is on completion, result, or you use …TIMES, or a number, choose the simple tense.

            She´s worked out four of the six problems.

           They’ve been to Scotland twice.

           How many times have you worn that dress?

And remember the most common mistakes in the use of the present perfect are…

• ·         Using the present simple instead: I know him since I was seven.
•       The incorrect use of FOR and SINCE:  since three years.
• ·         Making up inexistent tenses: How long have you studying Chinese?