Adding Business Days to a Date

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Introduction

Have you ever had to add days to a date and then make sure that the days are all business days?

Well, I have had to do this a number of times and when a junior developer asked me how I would do this, I thought I would share it with others. This will only work for a standard work week. By this, I mean Monday to Friday. Saturday and Sunday will be considered the weekend. The code is pretty easy to understand and if need be, should be simple to modify for your own particular use.

Using the Code

To simply add 2 business weeks to a start date, you call the function CalculateTenBusinessDaysFromInputDate and pass it the StartDate. This function will return you a date that has 10 business days from the StartDate. If the Startdate is a Saturday, we simply add 16 days to the StartDate passed in. If the StartDate is on a Sunday, then we add 15 days to the StartDate. For any other day of the week, we just add 14 days to the StartDate.

VB.NET

Public Function CalculateTenBusinessDaysFromInputDate(ByVal StartDate As Date) As Date
    'This simply adds at least 2 full weeks to the start date.

    Select Case StartDate.DayOfWeek

        Case DayOfWeek.Sunday
            'if the start date is not a sunday you need to add 
            '1 day to push it to a monday that is why the number is 15.
            Return StartDate.AddDays(15)
        Case DayOfWeek.Monday, DayOfWeek.Tuesday, _
		DayOfWeek.Wednesday, DayOfWeek.Thursday, DayOfWeek.Friday
            'if the start date is any other day then just add 14 days to the start date.
            Return StartDate.AddDays(14)
        Case DayOfWeek.Saturday
            'if the start date is on a Saturday you need to add 
            '2 days to push it to a monday that is why the number is 16.
            Return StartDate.AddDays(16)
        Case Else
            Return StartDate

    End Select

End Function

C#

public System.DateTime CalculateTenBusinessDaysFromInputDate(System.DateTime StartDate)
{
    //This simply adds at least 2 full weeks to the start date.

    switch (StartDate.DayOfWeek)
    {
        case DayOfWeek.Sunday:
            //if the start date is not a sunday you need to add 
            //1 day to push it to a monday that is why the number is 15.
            return StartDate.AddDays(15);
            break;
        case DayOfWeek.Monday:
        case DayOfWeek.Tuesday:
        case DayOfWeek.Wednesday:
        case DayOfWeek.Thursday:
        case DayOfWeek.Friday:
            //if the start date is any other day then just add 14 days to the start date.
            return StartDate.AddDays(14);
            break;
        case DayOfWeek.Saturday:
            //if the start date is on a Saturday you need to add 
            //2 days to push it to a monday that is why the number is 16.
            return StartDate.AddDays(16);
            break;
        default:
            return StartDate;
    }
}

This bit of code is a little bit more realistic. To use the CalculateBusinessDaysFromInputDate function, you need to supply both a StartDate and the number of business days that you want added to the StartDate. In CalculateBusinessDaysFromInputDate, we first check to see if the StartDate is a Saturday or a Sunday. If so, then I knock the number of business days down by one. I do this because we don't want the resulting date to be 11 business days out. NOTE: I did not do this in the CalculateTenBusinessDaysFromInputDate. For instance if the StartDate is a Monday and we added 12 business days to it, then the result should be on a Wednesday. Before we return the resulting date, we need to make sure that the date is not a weekend. If it is, then I move the date to the next Monday. You can also move the date back to the preceeding Friday by simply using the .AddDays() Date function and pass in a negative number. i.e. .AddDays(-2).

VB.NET

Public Function CalculateBusinessDaysFromInputDate_
	(ByVal StartDate As Date, ByVal NumberOfBusinessDays As Integer) As Date
    'Knock the start date down one day if it is on a weekend.
    If StartDate.DayOfWeek = DayOfWeek.Saturday Or StartDate.DayOfWeek = _
	DayOfWeek.Sunday Then
        NumberOfBusinessDays -= 1
    End If
    
    For index = 1 To NumberOfBusinessDays
        Select Case StartDate.DayOfWeek
            Case DayOfWeek.Sunday
                StartDate = StartDate.AddDays(2)
            Case DayOfWeek.Monday, DayOfWeek.Tuesday, DayOfWeek.Wednesday, _
				DayOfWeek.Thursday, DayOfWeek.Friday
                StartDate = StartDate.AddDays(1)
            Case DayOfWeek.Saturday
                StartDate = StartDate.AddDays(3)
                
        End Select
        
    Next
    
    'check to see if the end date is on a weekend.
    'If so move it ahead to Monday.
    'You could also bump it back to the Friday before if you desired to. 
    'Just change the code to -2 and -1.
    If StartDate.DayOfWeek = DayOfWeek.Saturday Then
        StartDate = StartDate.AddDays(2)
    ElseIf StartDate.DayOfWeek = DayOfWeek.Sunday Then
        StartDate = StartDate.AddDays(1)
    End If
    
    Return StartDate
    
End Function

C#

public System.DateTime CalculateBusinessDaysFromInputDate
	(System.DateTime StartDate, int NumberOfBusinessDays)
    {
        //Knock the start date down one day if it is on a weekend.
        if (StartDate.DayOfWeek == DayOfWeek.Saturday | 
			StartDate.DayOfWeek == DayOfWeek.Sunday)
        {
            NumberOfBusinessDays -= 1;
        }
        
        int index = 0;
        
        for (index = 1; index <= NumberOfBusinessDays; index++)
        {
            switch (StartDate.DayOfWeek)
            {
                case DayOfWeek.Sunday:
                    StartDate = StartDate.AddDays(2);
                    break;
                case DayOfWeek.Monday:
                case DayOfWeek.Tuesday:
                case DayOfWeek.Wednesday:
                case DayOfWeek.Thursday:
                case DayOfWeek.Friday:
                    StartDate = StartDate.AddDays(1);
                    break;
                case DayOfWeek.Saturday:
                    StartDate = StartDate.AddDays(3);
                    break;
            }
        }
        
        //check to see if the end date is on a weekend.
        //If so move it ahead to Monday.
        //You could also bump it back to the Friday before if you desired to. 
        //Just change the code to -2 and -1.
        if (StartDate.DayOfWeek == DayOfWeek.Saturday)
        {
            StartDate = StartDate.AddDays(2);
        }
        else if (StartDate.DayOfWeek == DayOfWeek.Sunday)
        {
            StartDate = StartDate.AddDays(1);
        }
        
        return StartDate;
    }

Points of Interest

This is a very simple way to calculate business days. There is no big algorithm associated with it.
If you need to figure out days in the past, this will work as well.  I hope this helps in some small way.

History

• 28^th October, 2009: Initial version