THE PRESENT CONTINUOUS TENSE

The present continuous is used for temporary actions or events going on at or around the time of speaking.
Look at the examples given below.
'The electrician is mending a fuse.'
'It's snowing.'

It is used for self-made schedules, generally for the not too distant future.

'Lucy's leaving for Bangkok after lunch.'
'Danny and Chelsea are getting married in June.'

It is also used for longer-term enterprises.

'He's studying hard to become a doctor.'
'Joe Liebermann's running for President.'

Used with adverbs of (high) frequency to express disproval of annoying habits.

'He is always complaining.'
'She's forever losing her keys.'

The present continuous must be used with 'have' when it is an action verb.

'She is having another baby.'
'She is having filet steak for dinner.'
'She is having a heart attack.'


Source :http://www.davidappleyard.com/english/tenses.htm#Present%20continuous