countdown timer using swift StackOverflow
@IBAction func start(sender: UIButton) { self.timer = Timer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(ViewController.update(_:)), userInfo: nil, repeats: true) NSRunLoop.currentRunLoop().addTimer(self.timer, forMode: NSRunLoopCommonModes) startTime = NSDate() // new instance variable that you would need to add. } func update() { let elapsedTime = NSDate().timeIntervalSinceDate(startTime) let currTime = totalTime - elapsedTime //total time is an instance variable that is the total amount of time in seconds that you want countDown.text = String(currTime) if currTime < 0 { timer.invalidate() //do other stuff that you need to do when time runs out. } }