بسم الله الرحمن الرحيم
You may pay the zakah of the nisab money before one year completes over it and when you calculate the zakah after passing the year then deduct the amount of zakah which you have already paid. It is not necessary to pay its zakah of again.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.