Adding Days to a Date but Excluding Weekends

Question

Given a date how can I add a number of days to it, but exclude weekends. For example, given 11/12/2008 (Wednesday) and adding five will result in 11/19/2008 (Wednesday) rather than 11/17/2008 (Monday).

I can think of a simple solution like looping through each day to add and checking to see if it is a weekend, but I'd like to see if there is something more elegant. I'd also be interested in any F# solution.

Solution 1

using Fluent DateTime https://github.com/FluentDateTime/FluentDateTime

var dateTime = DateTime.Now.AddBusinessDays(4);

Solution 2

public DateTime AddBusinessDays(DateTime dt, int nDays)
{
    int weeks = nDays / 5;
    nDays %= 5;
    while(dt.DayOfWeek == DayOfWeek.Saturday || dt.DayOfWeek == DayOfWeek.Sunday)
        dt = dt.AddDays(1);

    while (nDays-- > 0)
    {
        dt = dt.AddDays(1);
        if (dt.DayOfWeek == DayOfWeek.Saturday)
            dt = dt.AddDays(2);
    }
    return dt.AddDays(weeks*7);
}

Solution 3

Without over-complicating the algorithm, you could just create an extension method like this:

public static DateTime AddWorkingDays(this DateTime date, int daysToAdd)
{
    while (daysToAdd > 0)
    {
        date = date.AddDays(1);

        if (date.DayOfWeek != DayOfWeek.Saturday && date.DayOfWeek != DayOfWeek.Sunday)
        {
            daysToAdd -= 1;
        }
    }

    return date;
}

Solution 4

I would use this extension, remember since it is an extension method to put it in a static class.

Usage:

var dateTime = DateTime.Now.AddBusinessDays(5);

Code:

namespace ExtensionMethods
{
    public static class MyExtensionMethods
    {
        public static DateTime AddBusinessDays(this DateTime current, int days)
        {
            var sign = Math.Sign(days);
            var unsignedDays = Math.Abs(days);
            for (var i = 0; i < unsignedDays; i++)
            {
                do
                {
                    current = current.AddDays(sign);
                } while (current.DayOfWeek == DayOfWeek.Saturday ||
                         current.DayOfWeek == DayOfWeek.Sunday);
            }
            return current;
        }
    }
}

Source:

https://github.com/FluentDateTime/FluentDateTime/blob/master/src/FluentDateTime/DateTime/DateTimeExtensions.cs

Solution 5

int daysToAdd = weekDaysToAdd + ((weekDaysToAdd / 5) * 2) + (((origDate.DOW + (weekDaysToAdd % 5)) >= 5) ? 2 : 0);

To wit; the number of "real" days to add is the number of weekdays you're specifying, plus the number of complete weeks that are in that total (hence the weekDaysToAdd / 5) times two (two days in the weekend); plus a potential offset of two days if the original day of the week plus the number of weekdays to add "within" the week (hence the weekDaysToAdd mod 5) is greater than or equal to 5 (i.e. is a weekend day).

Note: this works assuming that 0 = Monday, 2 = Tuesday, ... 6 = Sunday. Also; this does not work on negative weekday intervals.

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