How do I pay zakat on an amount of 386 dinars if the original amount (3386 dinars) has been held for a full year, knowing that the current nisab is one thousand dinars?

The nisab (minimum threshold) for currencies is tied to the nisab of gold and silver, not to a specific number. So, whoever possesses money whose value reaches or exceeds the nisab of gold or silver, and a full year has passed on it, zakat becomes obligatory upon him. This is discharged by giving out one-quarter of one-tenth (2.5%) of the total amount, calculated by dividing the amount by forty. What is expressed as "25 in every thousand" is for ease of calculation and does not mean that amounts less than one thousand are not subject to zakat; rather, the entire amount is aggregated, and its zakat is then calculated and disbursed.