using System;

public class Program

{

    public static void Main()

    {

        for (var month = 1; month <= 12; month++)

        {

            var date = new DateTime(2019, month, 01);

            Console.WriteLine(string.Format("Date: {0}, Quarter: {1}, Financial Quarter: {2}", date, date.GetQuarter(), date.GetFinancialQuarter()));

        }

    }

}

​

public static class DateTimeExtensions

{

    public static int GetQuarter(this DateTime date)

    {

        return (date.Month + 2)/3;

    }

    public static int GetFinancialQuarter(this DateTime date)

    {

        return (date.AddMonths(-3).Month + 2)/3;

    }

}