Быстрая разница в датах в дни
let diffInDays = Calendar.current.dateComponents([.day], from: dateA, to: dateB).day
Annoying Angelfish
let diffInDays = Calendar.current.dateComponents([.day], from: dateA, to: dateB).daylet 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