What are the details of zakat on money upon which a year has passed, how is one-quarter of one-tenth calculated, and is there a minimum threshold for zakat below which zakat is not obligatory on the money?

Zakat is not obligatory unless the wealth reaches the nisab (minimum threshold) and a hawl (full lunar year) passes over it. The nisab for banknotes and similar assets is equivalent to the value of 85 grams of gold. To determine the nisab, one can consult scholars or follow gold prices. If the wealth reaches the nisab and a hawl passes over it, zakat becomes obligatory. The method for calculating a quarter of a tenth (2.5%) is by dividing the wealth by forty.