How is the value of gold zakat calculated when the price fluctuates during the hawl, knowing that the zakat payer pays his zakat at the beginning of Ramadan and calculates the value of gold according to its price at the time zakat becomes due?

The basic principle for Zakat on gold is that it should be paid from the gold itself, a quarter of a tenth (2.5%), if it reaches the nisab and a full year (hawl) has passed, without considering its price. However, if you wish to pay its value, then its price on the day Zakat is paid is considered, and fluctuations in its price before that day are not taken into account.