De or het kostenvermindering?

The correct Dutch article is:

de kostenvermindering

Rule Words ending in -ing: almost always de. See the rule

How to use kostenvermindering

the kostenverminderingde kostenvermindering
this kostenverminderingdeze kostenvermindering
that kostenverminderingdie kostenvermindering
our kostenverminderingonze kostenvermindering
your kostenverminderingjouw kostenvermindering
every kostenverminderingelke kostenvermindering
which kostenvermindering?welke kostenvermindering?
a big kostenvermindering / the big kostenverminderingeen grote kostenvermindering, de grote kostenvermindering