Converting date between timezones swift

runs more effeciently

extension Date {
    func convertToLocalTime(fromTimeZone timeZoneAbbreviation: String) -> Date? {
        if let timeZone = TimeZone(abbreviation: timeZoneAbbreviation) {
            let targetOffset = TimeInterval(timeZone.secondsFromGMT(for: self))
            let localOffeset = TimeInterval(TimeZone.autoupdatingCurrent.secondsFromGMT(for: self))

            return self.addingTimeInterval(targetOffset - localOffeset)
        }
    
        return nil
    }
}

Couldn't you just use your data formatter again with a different time zone and convert it? Such as

dateFormatter.timeZone = NSTimeZone(abbreviation: "GMT")
let gmtDate = dateFormatter.dateFromString(string: "your old date as string here")

Simpler version:

extension Date {
    func convertToTimeZone(initTimeZone: TimeZone, timeZone: TimeZone) -> Date {
         let delta = TimeInterval(timeZone.secondsFromGMT(for: self) - initTimeZone.secondsFromGMT(for: self))
         return addingTimeInterval(delta)
    }
}