وَإِنْ كَانَ مَالُهُ أَكْثَرَ مِنَ الدَّيْنِ، زَكَّى الْفَاضِلَ إِذَا بَلَغَ نِصَابًا.
Translation: If his wealth exceeds the debt, he pays zakat on the surplus when it reaches nisab.
If wealth exceeds the debt, only the surplus remaining after debt counts. Zakat is due when that remainder independently reaches nisab. It is not enough that the gross assets were above nisab before taking the qualifying debt into account.
For example, assess the relevant zakatable property and recognized debt separately. If the net balance falls below nisab, this general rule does not impose zakat.