Calculate the number of business days between two

Question

In C#, how can I calculate the number of business (or weekdays) days between two dates?

Answer 1

Here's some code for that purpose, with swedish holidays but you can adapt what holidays to count. Note that I added a limit you might want to remove, but it was for a web-based system and I didnt want anyone to enter some huge date to hog the process

  public static int GetWorkdays(DateTime from ,DateTime to)
    {
        int limit = 9999;
        int counter = 0;
        DateTime current = from;
        int result = 0;

        if (from > to)
        {
            DateTime temp = from;
            from = to;
            to = temp;
        }

        if (from >= to)
        {
            return 0;
        }


        while (current <= to && counter < limit)
        {
            if (IsSwedishWorkday(current))
            {
                result++;
            }
            current = current.AddDays(1);
            counter++;

        }
        return result;
    }


    public static bool IsSwedishWorkday(DateTime date)
    {
        return (!IsSwedishHoliday(date) && date.DayOfWeek != DayOfWeek.Saturday && date.DayOfWeek != DayOfWeek.Sunday);
    }

    public static bool IsSwedishHoliday(DateTime date)
    {
        return (
        IsSameDay(GetEpiphanyDay(date.Year), date) ||
        IsSameDay(GetMayDay(date.Year), date) ||
        IsSameDay(GetSwedishNationalDay(date.Year), date) ||
        IsSameDay(GetChristmasDay(date.Year), date) ||
        IsSameDay(GetBoxingDay(date.Year), date) ||
        IsSameDay(GetGoodFriday(date.Year), date) ||
        IsSameDay(GetAscensionDay(date.Year), date) ||
        IsSameDay(GetAllSaintsDay(date.Year), date) ||
        IsSameDay(GetMidsummersDay(date.Year), date) ||
        IsSameDay(GetPentecostDay(date.Year), date) ||
        IsSameDay(GetEasterMonday(date.Year), date) ||
        IsSameDay(GetNewYearsDay(date.Year), date) ||
        IsSameDay(GetEasterDay(date.Year), date)
        );
    }

    // Trettondagen
    public static DateTime GetEpiphanyDay(int year)
    {
        return new DateTime(year, 1, 6);
    }

    // Första maj
    public static DateTime GetMayDay(int year)
    {
        return new DateTime(year,5,1);
    }

    // Juldagen
    public static DateTime GetSwedishNationalDay(int year)
    {
        return new DateTime(year, 6, 6);
    }


    // Juldagen
    public static DateTime GetNewYearsDay(int year)
    {
        return new DateTime(year,1,1);
    }

    // Juldagen
    public static DateTime GetChristmasDay(int year)
    {
        return new DateTime(year,12,25);
    }

    // Annandag jul
    public static DateTime GetBoxingDay(int year)
    {
        return new DateTime(year, 12, 26);
    }


    // Långfredagen
    public static DateTime GetGoodFriday(int year)
    {
        return GetEasterDay(year).AddDays(-3);
    }

    // Kristi himmelsfärdsdag
    public static DateTime GetAscensionDay(int year)
    {
        return GetEasterDay(year).AddDays(5*7+4);
    }

    // Midsommar
    public static DateTime GetAllSaintsDay(int year)
    {
        DateTime result = new DateTime(year,10,31);
        while (result.DayOfWeek != DayOfWeek.Saturday)
        {
            result = result.AddDays(1);
        }
        return result;
    }

    // Midsommar
    public static DateTime GetMidsummersDay(int year)
    {
        DateTime result = new DateTime(year, 6, 20);
        while (result.DayOfWeek != DayOfWeek.Saturday)
        {
            result = result.AddDays(1);
        }
        return result;
    }

    // Pingstdagen
    public static DateTime GetPentecostDay(int year)
    {
        return GetEasterDay(year).AddDays(7 * 7);
    }

    // Annandag påsk
    public static DateTime GetEasterMonday(int year)
    {
        return GetEasterDay(year).AddDays(1);
    }
    public static DateTime GetEasterDay(int y)
    {
        double c;
        double n;
        double k;
        double i;
        double j;
        double l;
        double m;
        double d;
        c = System.Math.Floor(y / 100.0);
        n = y - 19 * System.Math.Floor(y / 19.0);
        k = System.Math.Floor((c - 17) / 25.0);
        i = c - System.Math.Floor(c / 4) - System.Math.Floor((c - k) / 3) + 19 * n + 15;
        i = i - 30 * System.Math.Floor(i / 30);
        i = i - System.Math.Floor(i / 28) * (1 - System.Math.Floor(i / 28) * System.Math.Floor(29 / (i + 1)) * System.Math.Floor((21 - n) / 11));
        j = y + System.Math.Floor(y / 4.0) + i + 2 - c + System.Math.Floor(c / 4);
        j = j - 7 * System.Math.Floor(j / 7);
        l = i - j;
        m = 3 + System.Math.Floor((l + 40) / 44);// month
        d = l + 28 - 31 * System.Math.Floor(m / 4);// day

        double days = ((m == 3) ? d : d + 31);

        DateTime result = new DateTime(y, 3, 1).AddDays(days-1);

        return result;
    }

Answer 2

I'll just share my solution. It worked for me, maybe I just don't notice/know that theres a bug. I started by getting the first incomplete week if there's any. a complete week was from sunday for saturday, so if the (int)_now.DayOfWeek was not 0(Sunday), the first week was incomplete.

I just subtract 1 to first weeks count for the first week's saturday then add it to new count;

Then I get the last incomplete week, then subtract 1 for it's sunday then add to new count.

Then finally, the number of complete weeks multiply by 5(weekdays) was added to new count.

public int RemoveNonWorkingDays(int numberOfDays){

            int workingDays = 0;

            int firstWeek = 7 - (int)_now.DayOfWeek;

            if(firstWeek < 7){

                if(firstWeek > numberOfDays)
                    return numberOfDays;

                workingDays += firstWeek-1;
                numberOfDays -= firstWeek;
            }


            int lastWeek = numberOfDays % 7;

            if(lastWeek > 0){

                numberOfDays -= lastWeek;
                workingDays += lastWeek - 1;

            }

            workingDays += (numberOfDays/7)*5;

            return workingDays;
        }

Answer 3

This solution avoids iteration, works for both +ve and -ve weekday differences and includes a unit test suite to regression against the slower method of counting weekdays. I've also include a concise method to add weekdays also works in the same non-iterative way.

Unit tests cover a few thousand date combinations in order to exhaustively test all start/end weekday combinations with both small and large date ranges.

Important: We make the assumption that we are counting days by excluding the start date and including the end date. This is important when counting weekdays as the specific start/end days that you include/exclude affect the result. This also ensures that the difference between two equal days is always zero and that we only include full working days as typically you want the answer to be correct for any time on the current start date (often today) and include the full end date (e.g. a due date).

NOTE: This code needs an additional adjustment for holidays but in keeping with the above assumption, this code must exclude holidays on the start date.

Add weekdays:

private static readonly int[,] _addOffset = 
{
  // 0  1  2  3  4
    {0, 1, 2, 3, 4}, // Su  0
    {0, 1, 2, 3, 4}, // M   1
    {0, 1, 2, 3, 6}, // Tu  2
    {0, 1, 4, 5, 6}, // W   3
    {0, 1, 4, 5, 6}, // Th  4
    {0, 3, 4, 5, 6}, // F   5
    {0, 2, 3, 4, 5}, // Sa  6
};

public static DateTime AddWeekdays(this DateTime date, int weekdays)
{
    int extraDays = weekdays % 5;
    int addDays = weekdays >= 0
        ? (weekdays / 5) * 7 + _addOffset[(int)date.DayOfWeek, extraDays]
        : (weekdays / 5) * 7 - _addOffset[6 - (int)date.DayOfWeek, -extraDays];
    return date.AddDays(addDays);
}

Compute weekday difference:

static readonly int[,] _diffOffset = 
{
  // Su M  Tu W  Th F  Sa
    {0, 1, 2, 3, 4, 5, 5}, // Su
    {4, 0, 1, 2, 3, 4, 4}, // M 
    {3, 4, 0, 1, 2, 3, 3}, // Tu
    {2, 3, 4, 0, 1, 2, 2}, // W 
    {1, 2, 3, 4, 0, 1, 1}, // Th
    {0, 1, 2, 3, 4, 0, 0}, // F 
    {0, 1, 2, 3, 4, 5, 0}, // Sa
};

public static int GetWeekdaysDiff(this DateTime dtStart, DateTime dtEnd)
{
    int daysDiff = (int)(dtEnd - dtStart).TotalDays;
    return daysDiff >= 0
        ? 5 * (daysDiff / 7) + _diffOffset[(int) dtStart.DayOfWeek, (int) dtEnd.DayOfWeek]
        : 5 * (daysDiff / 7) - _diffOffset[6 - (int) dtStart.DayOfWeek, 6 - (int) dtEnd.DayOfWeek];
}

I found that most other solutions on stack overflow were either slow (iterative) or overly complex and many were just plain incorrect. Moral of the story is ... Don't trust it unless you've exhaustively tested it!!

Unit tests based on NUnit Combinatorial testing and ShouldBe NUnit extension.

[TestFixture]
public class DateTimeExtensionsTests
{
    /// <summary>
    /// Exclude start date, Include end date
    /// </summary>
    /// <param name="dtStart"></param>
    /// <param name="dtEnd"></param>
    /// <returns></returns>
    private IEnumerable<DateTime> GetDateRange(DateTime dtStart, DateTime dtEnd)
    {
        Console.WriteLine(@"dtStart={0:yy-MMM-dd ffffd}, dtEnd={1:yy-MMM-dd ffffd}", dtStart, dtEnd);

        TimeSpan diff = dtEnd - dtStart;
        Console.WriteLine(diff);

        if (dtStart <= dtEnd)
        {
            for (DateTime dt = dtStart.AddDays(1); dt <= dtEnd; dt = dt.AddDays(1))
            {
                Console.WriteLine(@"dt={0:yy-MMM-dd ffffd}", dt);
                yield return dt;
            }
        }
        else
        {
            for (DateTime dt = dtStart.AddDays(-1); dt >= dtEnd; dt = dt.AddDays(-1))
            {
                Console.WriteLine(@"dt={0:yy-MMM-dd ffffd}", dt);
                yield return dt;
            }
        }
    }

    [Test, Combinatorial]
    public void TestGetWeekdaysDiff(
        [Values(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 20, 30)]
        int startDay,
        [Values(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 20, 30)]
        int endDay,
        [Values(7)]
        int startMonth,
        [Values(7)]
        int endMonth)
    {
        // Arrange
        DateTime dtStart = new DateTime(2016, startMonth, startDay);
        DateTime dtEnd = new DateTime(2016, endMonth, endDay);

        int nDays = GetDateRange(dtStart, dtEnd)
            .Count(dt => dt.DayOfWeek != DayOfWeek.Saturday && dt.DayOfWeek != DayOfWeek.Sunday);

        if (dtEnd < dtStart) nDays = -nDays;

        Console.WriteLine(@"countBusDays={0}", nDays);

        // Act / Assert
        dtStart.GetWeekdaysDiff(dtEnd).ShouldBe(nDays);
    }

    [Test, Combinatorial]
    public void TestAddWeekdays(
        [Values(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 20, 30)]
        int startDay,
        [Values(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 20, 30)]
        int weekdays)
    {
        DateTime dtStart = new DateTime(2016, 7, startDay);
        DateTime dtEnd1 = dtStart.AddWeekdays(weekdays);     // ADD
        dtStart.GetWeekdaysDiff(dtEnd1).ShouldBe(weekdays);  

        DateTime dtEnd2 = dtStart.AddWeekdays(-weekdays);    // SUBTRACT
        dtStart.GetWeekdaysDiff(dtEnd2).ShouldBe(-weekdays);
    }
}

Answer 4

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            DateTime start = new DateTime(2014, 1, 1);
            DateTime stop = new DateTime(2014, 12, 31);

            int totalWorkingDays = GetNumberOfWorkingDays(start, stop);

            Console.WriteLine("There are {0} working days.", totalWorkingDays);
        }

        private static int GetNumberOfWorkingDays(DateTime start, DateTime stop)
        {
            TimeSpan interval = stop - start;

            int totalWeek = interval.Days / 7;
            int totalWorkingDays = 5 * totalWeek;

            int remainingDays = interval.Days % 7;


            for (int i = 0; i <= remainingDays; i++)
            {
                DayOfWeek test = (DayOfWeek)(((int)start.DayOfWeek + i) % 7);
                if (test >= DayOfWeek.Monday && test <= DayOfWeek.Friday)
                    totalWorkingDays++;
            }

            return totalWorkingDays;
        }
    }
}

Answer 5

Here is the function which we can use to calculate business days between two date. I'm not using holiday list as it can vary accross country/region.

If we want to use it anyway we can take third argument as list of holiday and before incrementing count we should check that list does not contains d

public static int GetBussinessDaysBetweenTwoDates(DateTime StartDate,   DateTime EndDate)
    {
        if (StartDate > EndDate)
            return -1;

        int bd = 0;

        for (DateTime d = StartDate; d < EndDate; d = d.AddDays(1))
        {
            if (d.DayOfWeek != DayOfWeek.Saturday && d.DayOfWeek != DayOfWeek.Sunday)
                bd++;
        }

        return bd;
    }

Answer 6

 public enum NonWorkingDays { SaturdaySunday = 0, FridaySaturday = 1 };
        public int getBusinessDates(DateTime dateSt, DateTime dateNd, NonWorkingDays nonWorkingDays = NonWorkingDays.SaturdaySunday)
        {
            List<DateTime> datelist = new List<DateTime>();
            while (dateSt.Date < dateNd.Date)
            {
                datelist.Add((dateSt = dateSt.AddDays(1)));
            }
            if (nonWorkingDays == NonWorkingDays.SaturdaySunday)
            {
                return datelist.Count(d => d.DayOfWeek != DayOfWeek.Saturday &&
                       d.DayOfWeek != DayOfWeek.Friday);
            }
            else
            {
                return datelist.Count(d => d.DayOfWeek != DayOfWeek.Friday &&
                       d.DayOfWeek != DayOfWeek.Saturday);
            }
        }