De or het efficiencykorting?

The correct Dutch article is:

de efficiencykorting

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

How to use efficiencykorting

the efficiencykortingde efficiencykorting
this efficiencykortingdeze efficiencykorting
that efficiencykortingdie efficiencykorting
our efficiencykortingonze efficiencykorting
your efficiencykortingjouw efficiencykorting
every efficiencykortingelke efficiencykorting
which efficiencykorting?welke efficiencykorting?
a big efficiencykorting / the big efficiencykortingeen grote efficiencykorting, de grote efficiencykorting