Verifying logic for counting days between two dates excluding weekends

Question

The goal is to calculate the total number of leave days taken by all employees, broken down by month and year, ensuring weekends are not included in the count . The summation of leave days is returning incorrect values.

public double CalculateLeaveDaysForPeriod(List<EmployeeInfoDto> staffMembers, DateTime periodStart, DateTime periodEnd)
{
    double totalLeaveDays = 0;

    foreach (var staffMember in staffMembers)
    {
        foreach (var leaveRequest in staffMember.LeaveRequests)
        {
            DateTime leaveStartDate = leaveRequest.StartDate;
            DateTime leaveEndDate = leaveRequest.EndDate;

            DateTime validStartDate = leaveStartDate > periodStart ? leaveStartDate : periodStart;
            DateTime validEndDate = leaveEndDate < periodEnd ? leaveEndDate : periodEnd;

            if (validStartDate < validEndDate)
            {
                for (DateTime currentDay = validStartDate; currentDay <= validEndDate; currentDay = currentDay.AddDays(1))
                {
                    if (currentDay.DayOfWeek != DayOfWeek.Saturday && currentDay.DayOfWeek != DayOfWeek.Sunday)
                    {
                        totalLeaveDays++;
                    }
                }
            }
        }
    }
    return totalLeaveDays;
}

 public double GetLeaveDaysForCurrentMonth(List<EmployeeInfoDto> employees)
{
    var currentDate = DateTime.Now;
    var startOfMonth = new DateTime(currentDate.Year, currentDate.Month, 1); 
    var endOfMonth = startOfMonth.AddMonths(1).AddDays(-1); 

    return GetLeaveDaysForTimePeriod(employees, startOfMonth, endOfMonth);
}

public double GetLeaveDaysForCurrentYear(List<EmployeeInfoDto> employees)
{
    var currentDate = DateTime.Now;
    var startOfYear = new DateTime(currentDate.Year, 1, 1); 
    var endOfYear = new DateTime(currentDate.Year, 12, 31); 

    return GetLeaveDaysForTimePeriod(employees, startOfYear, endOfYear);
}

Here’s an example of the JSON data I’m working with, showing the start and end dates for each employee:

 "leaveRequests": [
    {
      "startDate": "2025-01-07T23:00:00Z",
      "endDate": "2025-01-09T23:00:00Z"
    }
  ]
},
{
  "leaveRequests": [
    {
      "startDate": "2025-01-05T23:00:00Z",
      "endDate": "2025-01-17T23:00:00Z"
    }
  ]
},
{
  "leaveRequests": [
    {
      "startDate": "2025-01-08T23:00:00Z",
      "endDate": "2025-01-23T23:00:00Z"
    }
  ]
}

FYI The DateTime class has this nice static method: DateTime.DaysInMonth(year, month); — Steve
– Steve, Commented Jan 10 at 22:19
Maybe you should use if (validStartDate <= validEndDate)? Because in the code that follows it, you also use <=. Or if it should stay < then maybe use < in both places. — Peter B
– Peter B, Commented Jan 10 at 22:57

Gustav · Accepted Answer · 2025-01-11 08:53:49Z

The time parts may cause you trouble.

This works for me:

//DateTime leaveStartDate = new DateTime(2025, 1, 7, 23, 0, 0);
//DateTime leaveEndDate = new DateTime(2025, 1, 9, 23, 0, 0);

//DateTime leaveStartDate = new DateTime(2025, 1, 5, 23, 0, 0);
//DateTime leaveEndDate = new DateTime(2025, 1, 17, 23, 0, 0);

//DateTime leaveStartDate = new DateTime(2025, 1, 8, 23, 0, 0);
//DateTime leaveEndDate = new DateTime(2025, 1, 23, 23, 0, 0);

DateTime leaveStartDate = new DateTime(2025, 1, 8, 23, 0, 0);
DateTime leaveEndDate = new DateTime(2025, 2, 4, 23, 0, 0);

//DateTime periodStartDate = new DateTime(2025, 1, 1, 0, 0, 0);
//DateTime periodEndDate = new DateTime(2025, 1, 31, 0, 0, 0);

DateTime periodStartDate = new DateTime(2025, 2, 1, 0, 0, 0);
DateTime periodEndDate = new DateTime(2025, 2, 28, 0, 0, 0);

DateTime startDate = leaveStartDate.Date > periodStartDate ? leaveStartDate.Date : periodStartDate;
DateTime endDate = leaveEndDate.Date < periodEndDate ? leaveEndDate.Date : periodEndDate;

DateTime currentDate = startDate;
int totalLeaveDays = 0;

// To not include endDate as a leave day, use:
// currentDate < endDate)
while (currentDate <= endDate)
{
    if (currentDate.DayOfWeek != DayOfWeek.Saturday && currentDate.DayOfWeek != DayOfWeek.Sunday)
    {
        totalLeaveDays++;
    }
    currentDate = currentDate.AddDays(1);
};

Console.WriteLine(totalLeaveDays.ToString());
// 3
// 10
// 12

Elec1 · Accepted Answer · 2025-01-10 22:48:38Z

0

Use the Subtraction method of the DateTime class for computing the number days for your time interval. Divide the number of days by 7 and multiply the result by 2. That gives you the number of leave days of the full 7-day weeks. Divide number of days modulo 7 ( % 7 instead of / 7). This gives you the remaining days which range from 0 through 6. Count the number of leave days contained in this result which is a number in the range from 0 through 2. Add this number to the number of leave days of the complete weeks and you are done.

answered Jan 10 at 22:48

Elec1

2843 silver badges12 bronze badges

Collectives™ on Stack Overflow

Verifying logic for counting days between two dates excluding weekends

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related