Harnessing the Potential of WEEKNUM
Channel: Biddrup 
Date: 13/06/2023

When working with the WEEKNUM function in Google Sheets, here are some important things to know:

1. Syntax: The WEEKNUM function takes two arguments:
   - date: The date for which you want to determine the week number. It can be a reference to a cell containing a date, a function returning a date type, or a number.
   - type (optional): This argument specifies the day that a week starts on and the system used for determining the first week of the year. If omitted, the default value is 1 (Sunday).

2. Date format: It is recommended to use the DATE function or a recognized date format rather than text values when providing the date argument. Using text values may lead to errors.

3. Week numbering systems: There are two week numbering systems used by the WEEKNUM function:
   - System 1: The first week of the year is considered to be the week containing January 1, which is numbered as week 1.
   - System 2: The first week of the year is considered to be the week containing the first Thursday of the year, which is numbered as week 1. This system follows ISO 8601, also known as the European system for numbering weeks.

4. Week start and end days: The start and end days of a week depend on the type argument. Here are the start and end days for each type:
   - Type 1 (or omitted): Week begins on Sunday and ends on Saturday (System 1).
   - Type 2: Week begins on Monday and ends on Sunday (System 1).
   - Type 11: Same as Type 2.
   - Type 12: Week begins on Tuesday and ends on Monday (System 1).
   - Type 13: Week begins on Wednesday and ends on Tuesday (System 1).
   - Type 14: Week begins on Thursday and ends on Wednesday (System 1).
   - Type 15: Week begins on Friday and ends on Thursday (System 1).
   - Type 16: Week begins on Saturday and ends on Friday (System 1).
   - Type 17: Week begins on Sunday and ends on Saturday (System 1).
   - Type 21: Week begins on Monday and ends on Sunday (System 2).

By understanding these concepts, you can use the WEEKNUM function effectively to calculate the week number based on the specified date and week numbering system.

1. Workforce Scheduling:
   - Assuming the week numbers are in column A and employee names are in column B, you can use the following formula to assign employees to shifts based on the week number:
     ```
     =IF(MOD(WEEKNUM(A2), 2) = 0, "Shift A", "Shift B")
     ```
     This formula checks if the week number is even (Shift A) or odd (Shift B) and assigns the corresponding shift to the employee.

2. Project Planning:
   - Assuming the start date of the project is in cell A2 and the task completion dates are in column B, you can use the following formula to calculate the week number for each task:
     ```
     =WEEKNUM(B2) - WEEKNUM($A$2) + 1
     ```
     This formula subtracts the week number of the project start date from the week number of each task completion date and adds 1 to get the week number of the task within the project.

3. Sales Analysis:
   - Assuming the sales dates are in column A and the corresponding sales amounts are in column B, you can use the following formula to calculate the total sales for each week:
     ```
     =SUMIF(WEEKNUM(A:A), week_number, B:B)
     ```
     Replace "week_number" with the specific week number you want to calculate the total sales for. This formula uses the SUMIF function to sum the sales amounts for all the dates that fall within the specified week.

4. Expense Tracking:
   - Assuming the expense dates are in column A and the corresponding expense amounts are in column B, you can use the following formula to calculate the total expenses for each week:
     ```
     =SUMIF(WEEKNUM(A:A), week_number, B:B)
     ```
     Replace "week_number" with the specific week number you want to calculate the total expenses for. This formula uses the SUMIF function to sum the expense amounts for all the dates that fall within the specified week.

5. Fitness and Health Tracking:
   - Assuming the date of each fitness or health measurement is in column A and the corresponding measurement data is in column B, you can use the following formula to calculate the average measurement for each week:
     ```
     =AVERAGEIF(WEEKNUM(A:A), week_number, B:B)
     ```
     Replace "week_number" with the specific week number you want to calculate the average measurement for. This formula uses the AVERAGEIF function to calculate the average measurement data for all the dates that fall within the specified week.

6. Event Planning:
   - Assuming the start date of the event planning process is in cell A2 and the tasks assigned to each week are in column B, you can use the following formula to assign tasks based on the week number:
     ```
     =IF(WEEKNUM(B2) = WEEKNUM($A$2), "This Week", "Next Week")
     ```
     This formula checks if the week number of the task matches the week number of the event planning start date and assigns "This Week" or "Next Week" accordingly..