Extends projections to include 50 per cent of loss (8)
I believe the answer is:
prolongs
'extends' is the definition.
('prolong' can be a synonym of 'extend')
'projections to include 50 per cent of loss' is the wordplay.
'projections' becomes 'prongs' (prong is a kind of projection).
'to include' is an insertion indicator.
'g0 per cent of' means to take half the letters.
'loss' with half the letters taken is 'lo'.
'prongs' enclosing 'lo' is 'PROLONGS'.
(Other definitions for prolongs that I've seen before include "Extends the duration of" , "Lengthens in time. draws out" , "keeps going" .)