Can zakat be given before its due time?

Just like with fasting and pilgrimage, the lunar calendar is used for zakat. For zakat to become obligatory, a full lunar year must pass over wealth that meets the nisab threshold. However, if the owner wishes, zakat on wealth that has reached the nisab can be given before the year is completed. (Kâsânî, Bedâ’i, 2/50-51; Ibn al-Humam, Fath al-Qadir, 2/206)

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu