Swift 3 - find number of calendar days between two dates

In Swift 5 there is a simple one-liner to get the number of days (or any other DateComponent) between two dates:

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

Note: As pointed out in the comments, this solution measures the 24h periods and therefore requires at least 24h between dateA and dateB.

If any one want to do it more specifically follow Below Steps

1.Add this Date Extension

extension Date {
    /// Returns the amount of years from another date
func years(from date: Date) -> Int {
    return Calendar.current.dateComponents([.year], from: date, to: self).year ?? 0
}
/// Returns the amount of months from another date
func months(from date: Date) -> Int {
    return Calendar.current.dateComponents([.month], from: date, to: self).month ?? 0
}
/// Returns the amount of weeks from another date
func weeks(from date: Date) -> Int {
    return Calendar.current.dateComponents([.weekOfMonth], from: date, to: self).weekOfMonth ?? 0
}
/// Returns the amount of days from another date
func days(from date: Date) -> Int {
    return Calendar.current.dateComponents([.day], from: date, to: self).day ?? 0
}
/// Returns the amount of hours from another date
func hours(from date: Date) -> Int {
    return Calendar.current.dateComponents([.hour], from: date, to: self).hour ?? 0
}
/// Returns the amount of minutes from another date
func minutes(from date: Date) -> Int {
    return Calendar.current.dateComponents([.minute], from: date, to: self).minute ?? 0
}
/// Returns the amount of seconds from another date
func seconds(from date: Date) -> Int {
    return Calendar.current.dateComponents([.second], from: date, to: self).second ?? 0
}
/// Returns the amount of nanoseconds from another date
func nanoseconds(from date: Date) -> Int {
    return Calendar.current.dateComponents([.nanosecond], from: date, to: self).nanosecond ?? 0
}
/// Returns the a custom time interval description from another date
func offset(from date: Date) -> String {
    var result: String = ""
            if years(from: date)   > 0 { return "\(years(from: date))y"   }
            if months(from: date)  > 0 { return "\(months(from: date))M"  }
            if weeks(from: date)   > 0 { return "\(weeks(from: date))w"   }
    if seconds(from: date) > 0 { return "\(seconds(from: date))" }
            if days(from: date)    > 0 { result = result + " " + "\(days(from: date)) D" }
            if hours(from: date)   > 0 { result = result + " " + "\(hours(from: date)) H" }
            if minutes(from: date) > 0 { result = result + " " + "\(minutes(from: date)) M" }
           if seconds(from: date) > 0 { return "\(seconds(from: date))" }
    return ""
 }
}

2.Define it in globally

 fileprivate var timer: Timer?

3.Call this Method in viewDidLoad or where ever you want

override func viewDidLoad() {
    super.viewDidLoad()
    self.getRemainingTime()
} 

4.Usage

fileprivate func getRemainingTime() {
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"

    let startDate = "2018-06-02 10:11:12"
    let currentDate = dateFormatter.string(from: Date())

    if currentDate != startDate {
        timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: (#selector(calculateTime)), userInfo: nil, repeats: true)
        RunLoop.current.add(timer!, forMode: RunLoopMode.commonModes)
        timer?.fire()
    }
    else {
        self.timer?.invalidate()
        self.timer = nil
    }
}

func calculateTime() {
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"

    let stdate : String = "2018-06-02 10:11:12"
    let startDate = dateFormatter.date(from: stdate)!

    let currentDate = Date()

    let strTimer : String = startDate.offset(from: currentDate)
    if !strTimer.isEmpty {
        let stDay: String = "\((Int(strTimer)! % 31536000) / 86400)"
        let stHour: String = "\((Int(strTimer)! % 86400) / 3600)"
        let stMin: String = "\((Int(strTimer)! % 3600) / 60)"
        let stSec: String = "\(Int(strTimer)! % 60)"
        yourLabelOutlet.text = "Start In :\(stDay) Days \(stHour) Hours \(stMin) Minutes \(stSec) Seconds"
    }

}

Works like Charm You can Use every separate string to your UI Side, Enjoy

Turns out this is much simpler to do in Swift 3:

extension Date {    

    func interval(ofComponent comp: Calendar.Component, fromDate date: Date) -> Int {

        let currentCalendar = Calendar.current

        guard let start = currentCalendar.ordinality(of: comp, in: .era, for: date) else { return 0 }
        guard let end = currentCalendar.ordinality(of: comp, in: .era, for: self) else { return 0 }

        return end - start
    }
}

Edit

Comparing the ordinality of the two dates should be within the same era instead of the same year, since naturally the two dates may fall in different years.

Usage

let yesterday = Date(timeInterval: -86400, since: Date())
let tomorrow = Date(timeInterval: 86400, since: Date())


let diff = tomorrow.interval(ofComponent: .day, fromDate: yesterday)
// return 2

Swift 4 Version

let startDate = "2000-11-22"
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let formatedStartDate = dateFormatter.date(from: startDate)
let currentDate = Date()
let components = Set<Calendar.Component>([.second, .minute, .hour, .day, .month, .year])
let differenceOfDate = Calendar.current.dateComponents(components, from: formatedStartDate!, to: currentDate)

print (differenceOfDate)

Printed - year: 16 month: 10 day: 19 hour: 12 minute: 16 second: 42 isLeapMonth: false

swift4 calendar date