Is zakat due on money that has not been in one's possession for a full year if it is found with money that has reached the nisab and a full year has passed on it, and what is the amount of the nisab in US dollars?

It is permissible to combine money that has not completed a full year (if it was not derived from the first amount of money) with money that has completed a full year, and pay zakat on both together. Alternatively, one may wait until the second amount also completes a full year and then pay its zakat. The zakat threshold for paper currency is determined by equating it to gold (85 grams) or silver (595 grams), and it is more cautious to estimate it based on silver.