How is zakat handled for a sum of money to which another sum was added before a full year (hawl) passed on the second sum, with both being in the same bank account?

Funds acquired during the Zakat year, such as inheritance and salary, are not subject to Zakat until a full year has passed over them and they reach the nisab. One may designate a separate hawl (Zakat year) for each acquired fund, so its Zakat is distributed according to the passage of time. It is also permissible to pay the Zakat for acquired funds along with the Zakat for original funds, with the intention of expediting its Zakat. This is permissible and not obligatory.