The discount will be calculated automatically if there is a check mark  in the Izracunaj popust na racunu field  in the Purchases &amp; Payables Setup window and you do one of the following  on the purchase document:
Popust se izračuna samodejno, če je v oknu »Nastavitev nabave in obveznosti« potrjeno polje Izračunaj popust na računu  in če v nabavnem dokumentu naredite nekaj od tega: