Gerund or Progressive/Continuous

Both forms end in -ing. Nevertheless it is easy to find out whether it is a Gerund or a Progressive form.
These tenses are formed with von to be and the infinitive + - ing.

sentences	tense
He is reading a book.	Present Progressive
He was reading a book.	Past Progressive
He has been reading a book for three hours.	Present Perfect Progressive
He had been reading a book before Mary came in.	Past Perfect Progressive
He will be reading a book when I get home.	will-future Progressive
He will have been reading a book.	Future Perfect Progressive
He would be reading a book if he had time.	Conditional Progressive
He would have been reading a book if he had had time.	Conditional Perfect Progressive
A book is being read.	Present Progressive - Passive
A book was being read.	Past Progressive - Passive

The Gerund is formed only with infinitive + - ing.

sentence
Reading books is great fun.
He likes reading books.
He is looking forward to reading books at the weekend.
He is keen on reading books.
He is used to reading books.
What about reading books?
He likes the idea of reading books.
After reading the book, he went to bed.
I remember having read this book. - Passive