Yes, I'm talking about the 1000€ Arbeitnehmerpauschbetrag (also known as Werbungskostenpauschale). This is already deducted while calculating your monthly payme

Yes, I'm talking about the 1000€ Arbeitnehmerpauschbetrag (also known as Werbungskostenpauschale). This is already deducted while calculating your monthly payments, see § 39b Abs. 2 S. 5 Nr. 1 EStG. If you have the same income each month (and there haven't been changes in law during the year) each monthly payment covers exactly 1/12 of your income tax. So in that case, the December payment is the same. Do to different circumstances you might still get small sums back, as you noticed