How is the zakat calculated for a sum of money borrowed from a bank to build a house, then invested in trade and profited from, knowing that the loan is still being repaid in annual installments and accrues interest?

Borrowing with usury is a major sin that should not be committed. You must strive to rid yourself of this usurious loan as much as possible. If it is possible to pay it off in one lump sum, then that is obligatory. Otherwise, pay off what you owe in installments, along with repentance, seeking forgiveness, and increasing good deeds.

As for zakat, the debt is deducted from the principal and its profit at the end of the year, and what remains is subject to zakat if it reaches the nisab (minimum threshold) of 2.5%.