Is zakat obligatory on an end-of-service bonus that includes a portion of usurious interest, and how is it calculated, considering that there is no other income besides investment in an Islamic bank and a commercial project?

Firstly: It is not permissible to work in interest-based banks, and the money earned from them is forbidden and must be disposed of, unless the person was ignorant of the prohibition of working therein or was in need of the money. In such cases, it is permissible for him to take what he needs or to make it capital in a permissible business after repentance.

Secondly: Zakat is obligatory on bank deposits and their profits if the money reaches the Nisab and a full year has passed over it. One-quarter of a tenth (2.5%) must be given out. Zakat is obligatory on the bank deposit even if withdrawals are prohibited.

Thirdly: If the money with your friend is in trade goods, then they must be evaluated every year, and one-quarter of a tenth of the value of your share must be given out.

Fourthly: The savings fund may be permissible or impermissible.