Keeping the six fasts of Shawwal after keeping the fasts of Ramadaan equals to 360 days of fasting
Sayyiduna Abu Ayyub Ansaari Radhiyallahu Anhu mentions that Rasulullah Sallallahu Alayhi Wasallam said: “Whoever observed the fasts of Ramadhan, then follows them with the fasts of six days in the Month of Shawwal, he will be rewarded as if he fasted for the entire year.”(Muslim)
Note: The reward of each good deed is multiplied at least ten times. Therefore, thirty days of fast in Ramadaan equals three hundred days and the six fast of Shawwal equal sixty days. Thus, totalling to three hundred and sixty days, which is the total amount of days in a lunar year.