using System;

using System.Globalization;

​

public class Program

{

    public static void Main()

    {

        CalcStartDate( "12-01-2022", "11-18" );

        CalcStartDate( "10-29-2022", "11-18" );

        CalcStartDate( "10-11-2022", "10-01" ); 

        CalcStartDate( "10-11-2023", "10-01" ); 

    }

    private static void CalcStartDate(string stringDateTimeNow, string stringStartDate)

    {

        DateTime datetimeNow = DateTime.Parse(stringDateTimeNow, CultureInfo.InvariantCulture);

​

        DateTime startDate=DateTime.ParseExact(stringStartDate, "MM-dd", CultureInfo.InvariantCulture); 

        if (IsMonthDayLessThan( datetimeNow, startDate))

        {

            startDate = new DateTime( datetimeNow.Year - 1, startDate.Month, startDate.Day);

        }

        else

        {

            startDate = new DateTime( datetimeNow.Year, startDate.Month, startDate.Day);

        }

        Console.WriteLine("");

        Console.WriteLine("Now:       " + stringDateTimeNow + "     " + datetimeNow.ToString("MM/dd/yyyy HH:mm"));

        Console.WriteLine("StartDate: " + stringStartDate + "          " + startDate.ToString("MM/dd/yyyy HH:mm"));

    }

    private static bool IsMonthDayLessThan( DateTime timeSource, DateTime timeTarget)

    {

        return timeSource.Month < timeTarget.Month || (timeSource.Month == timeTarget.Month && timeSource.Day < timeTarget.Day);

    }

}