فَإِذَا كَانَتْ عِشْرِينَ مِثْقَالًا، وَحَالَ عَلَيْهَا الْحَوْلُ: فَفِيهَا نِصْفُ مِثْقَالٍ.
Translation: If it amounts to twenty mithqals and a year passes over it, half a mithqal is due.
Two conditions are stated together: the twenty-mithqal threshold and completion of the zakat year. When these and the other general conditions are met, the due amount is half a mithqal.