using System.Globalization;
static void Main(string[] args)
var dateTimeOffset = DateTimeOffset.UtcNow;
var dateString1 = dateTimeOffset.ToString();
var dateString2 = dateTimeOffset.ToString("O");
ParseDateIso8601(dateString1);
ParseDateIso8601(dateString2);
private static void ParseDateIso8601(string dateString)
var date = DateTimeOffset.ParseExact(dateString, "O", null, DateTimeStyles.RoundtripKind);
Console.WriteLine($"{dateString} IS in ISO-8601 format. Parsed Date - {date}");
Console.WriteLine($"{dateString} IS NOT in ISO-8601 format");