Check out example codes for "swift date difference in days". It will help you in understanding the concepts better.

Code Example 1

let diffInDays = Calendar.current.dateComponents([.day], from: dateA, to: dateB).day

Code Example 2

let calendar = Calendar.current

// Replace the hour (time) of both dates with 00:00
let date1 = calendar.startOfDay(for: firstDate)
let date2 = calendar.startOfDay(for: secondDate)

let components = calendar.dateComponents([.day], from: date1, to: date2)
return components.day

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