What are the rulings regarding Zakāt on money in the following cases: 1. The difference between the Gregorian and Hijri calendars in calculating the Hawl (one lunar year), and whether 11 extra days should be calculated, and whether Zakāt is to be paid on the old or new Niṣāb after 12 months have passed? 2. Does a new Hawl begin on the Hijri date corresponding to the current Gregorian date, or should the payment of Zakāt be brought forward? 3. The ruling on paying Zakāt in late installments, knowing that the zakāt payer is well-off? 4. Does the parents' non-compliance with some religious obligations, such as praying on time, abandoning congregational and Friday prayers, and watching forbidden things on television, affect the ruling on their Zakāt?

Firstly: The Nisab is the threshold at which wealth becomes subject to Zakat.

Secondly: There is no sin upon one who paid Zakat according to the Gregorian calendar out of ignorance. However, in the future, it must be paid according to the lunar calendar. One who knows this and delays payment incurs sin.

Thirdly: It is not permissible to pay Zakat in installments that are delayed beyond its due time. Rather, it must be paid on the day the hawl (one lunar year) is completed.

Fourthly: There is no need to re-pay past Zakat payments that were disbursed according to the Gregorian calendar, even though they were delayed from their prescribed time.

Fifthly: If it is confirmed that there is a difference between Zakat calculated by the Gregorian calendar and the lunar calendar, then the father must pay what he believes, to the best of his judgment, compensates for the Zakat of these differences for all the delayed years. He should act upon his best judgment in estimating the wealth and the number of years if he is uncertain. This delay must be remedied by correcting the hawl and converting the date to determine the correct Hijri date, and by promptly paying the delayed Zakat.