Is zakat obligatory for a government employee who owns nothing, supports his family and siblings, and how is zakat calculated on money accumulated during the year that has not yet reached its one-year anniversary (hawl)?

Zakat becomes obligatory on wealth if it reaches the nisab and a full Hijri year passes over it. The nisab is approximately equivalent to 595 grams of pure silver. If wealth reaches this amount, the Hijri year is calculated. If a full year passes without the wealth decreasing below the nisab, then zakat becomes obligatory on it. As for what is spent from the wealth during the year, there is no zakat on it.