how to calculate expiry date in c#

string[] expiryDateDbSplit = expiryDate.Split('-');
                            int expYrs = Convert.ToInt32(expiryDateDbSplit[0]);
                            int expMth = Convert.ToInt32(expiryDateDbSplit[1]);
                            int expDays = Convert.ToInt32(expiryDateDbSplit[2]);
                            DateTime start = new DateTime(expYrs, expMth, expDays);

                            int yrs = System.DateTime.Now.Year;
                            int month = System.DateTime.Now.Month;
                            int days = System.DateTime.Now.Day;
                            DateTime end = new DateTime(yrs, month, days);

                            TimeSpan difference = end - start; //create TimeSpan object
                            int totalDays = difference.Days;
                            int totalYears = (end.Year - start.Year);
                            if (totalDays <= 30)
                            {
                                penaltyAmt = 0;
                            }
                            else if (totalDays > 30 && totalDays <= 180)
                            {
                                penaltyAmt = 500;
                            }
                            else if (totalDays > 180)
                            {
                                if (totalYears > 0)
                                {
                                    penaltyAmt = 500 * totalYears;
                                }
                                else
                                {
                                    penaltyAmt = 500;
                                }
                            }