class SaveOverview(ListView, FormMixin):

    def get_form_kwargs(self):
        kwargs = super(SaveOverview, self).get_form_kwargs()
        kwargs["start_date"]=self.request.GET.get("start_date")
        return kwargs

# asta in form
start_date = kwargs.get('start_date', datetime.today().strftime('%Y-%m-%d'))
kwargs.pop("start_date")