# Power BI: Calculating Network Days in M Custom Columns

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Knowing the days between events is a fairly common reporting request because a lot of reporting is created to track SLA’s (service level agreement) and other KPI’s (key performance indicators). While getting the days between two dates is fairly easy to achieve, they tend to follow up and ask how many week days there are between two timed events. For example, one company may have a SLA to ship an order within three week days of the order being placed or else a discount is applied to the order. In this case, I would highly recommend that the company have software that calculates these days in the background and stores the actual week days between order date and ship date in a database. Unfortunately, many companies create policies like this without considering future reporting needs and these values have to be calculated on the backend.

Please note, this blog will not cover how to calculate business days (week days that are non-holidays) because that should be done upstream from Power BI in either an application or SQL stored proc that can get/set holidays dynamically (the date of Easter changes every year). International clients often have different holidays which can infinitely complicate the definition of a business day. Also, many coding languages have built in functions to get business days while Power BI does not (sadly, the Excel NETWORKDAYS() function is not currently in Power BI) . So for this, we will stick to excluding weekends and getting a count of the week days between two events.

### The Final Equation

To make it easier to read, SD means start date and ED means end date. SWD will mean the work week day of the start date and EWD means work week day of the end date. For example, if the order date was May 2nd 2022 and the ship date was May 4th 2022, then the SD = 5/2/2022, SWD = Monday/day 2 of the week, ED = 5/4/2022, and EWD = Wednesday/ day 4 of the week. But let’s say the SD was May 7th which is a Saturday. We would adjust this to be Friday/ day 6 of the week. I’ll put code below to show how to adjust the weekends to Friday before and how to adjust to the Monday after, but the GitHub file will align weekends to the Friday before.

Week days between = ( if SWD > EWD then (5 + EWD – SWD) else (EWD – SWD)) + (5 * ( Actual Days Between /7 rounded down))

In plain English: the week days between two dates starts by looking at if the start date is earlier in the week than the end date. If the start date is later in the week than the end date, then add five to the difference between their day of the week (for example, end day of Monday to start day of Wednesday would be 5 + 4-2). If the start date is earlier in the week than the end date, then take the difference between those two days of the week (start day Monday to end day Wednesday would be 4-2).

Next, take the actual days between your end and start date including weekends, divide that by seven then round down. That will give you the number of full weeks between your two days. Multiple that number by 5 to represent the five days within each of those weeks.

Finally, add those two numbers together to get your week days between the start and end dates.

### Building the Variables

To create that final equation, we will need to build a few extra columns in the Power Query Editor. For each one, we will click on “Transform Data”, go to the “Add Column” tab, then select “Custom Column”. This will open a window to type in some custom M code (yay another coding language!).

Don’t worry though, I have ya covered with the code you need for this demo. To start, identify your columns with your start date and end date. For this demo, we will have Start Date = Order Date and End Date = Ship Date. The code below will use StartDate and EndDate for these fields, but the GitHub file will use Order Date and Ship Date.

The code below will turn Saturday and Sunday into Friday:

Start Date Work Weekday =
Date.DayOfWeek(
(if (Date.DayOfWeek([StartDate],Day.Sunday)+1) = 1
if (Date.DayOfWeek([StartDate],Day.Sunday)+1) = 7
,Day.Sunday) +1
End Date Work Weekday =
Date.DayOfWeek(
(if (Date.DayOfWeek([EndDate],Day.Sunday)+1) = 1
if (Date.DayOfWeek([EndDate],Day.Sunday)+1) = 7
,Day.Sunday) +1

The code below will turn Saturday and Sunday into Monday

Start Date Work Weekday =
Date.DayOfWeek(
(if (Date.DayOfWeek([StartDate],Day.Sunday)+1) = 1
if (Date.DayOfWeek([StartDate],Day.Sunday)+1) = 7
,Day.Sunday) +1
End Date Work Weekday =
Date.DayOfWeek(
(if (Date.DayOfWeek([EndDate],Day.Sunday)+1) = 1
if (Date.DayOfWeek([EndDate],Day.Sunday)+1) = 7
,Day.Sunday) +1

Work Weekday =
Date.DayOfWeek( //sets us up to get the day of the week at the end of the formula
(if (Date.DayOfWeek([Date],Day.Sunday)+1) = 1 //if it's Sunday
then Date.AddDays([Date],-2) else //then go back two days to get Friday's date
if (Date.DayOfWeek([Date],Day.Sunday)+1) = 7 //if it's Saturday
then Date.AddDays([Date],-1) else [Date]) //then go back one day to get Thursday's date, otherwise give me the date
,Day.Sunday) +1 //now give me the day of the week for the date left from the previous if statements

Alrighty, the next building variable we will need for our equation is the actual days (including weekends).

Days Between = Duration.Days([EndDate]-[StartDate])

In our case though, there is a possibility that the orders have not shipped. To handle any errors where there is no EndDate or StartDate, use the equation below:

Days Between = if [EndDate] is null then null else
if [StartDate] is null then null else
Duration.Days([EndDate]-[StartDate])

Okay great, now we can put it all together using our new fields!

Weekdays Between =
( if [Start Date Work Weekday] > [End Date Work Weekday]
then ( 5 + [End Date Work Weekday] - [Start Date Work Weekday] )
else ( [End Date Work Weekday] - [Start Date Work Weekday] ))
+ ( 5 * ( Number.RoundDown ( [Days Between] / 7 )))

Boom all done! You made it through a lot of complicated M code, nice work! Below is the M used in the GitHub file so you can see how it will look in the advanced editor.

let
Source = Excel.Workbook(File.Contents("C:UsersKristynaHughesOneDrive - DataOnWheelsGitHubAdventureWorks Sales.xlsx"), null, true),
Sales_data_Sheet = Source{[Item="Sales_data",Kind="Sheet"]}[Data],
#"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"SalesOrderLineKey", Int64.Type}, {"ResellerKey", Int64.Type}, {"CustomerKey", Int64.Type}, {"ProductKey", Int64.Type}, {"OrderDateKey", Int64.Type}, {"DueDateKey", Int64.Type}, {"ShipDateKey", Int64.Type}, {"SalesTerritoryKey", Int64.Type}, {"Order Quantity", Int64.Type}, {"Unit Price", type number}, {"Extended Amount", type number}, {"Unit Price Discount Pct", Int64.Type}, {"Product Standard Cost", type number}, {"Total Product Cost", type number}, {"Sales Amount", type number}}),
#"Added Order Date" = Table.AddColumn(#"Changed Type", "Order Date", each Date.From( Text.Middle(Text.From([OrderDateKey]),4,2)&"/"& Text.End(Text.From([OrderDateKey]),2)&"/"& Text.Start(Text.From([OrderDateKey]),4)),type date),
(if (Date.DayOfWeek([Order Date],Day.Sunday)+1) = 1
if (Date.DayOfWeek([Order Date],Day.Sunday)+1) = 7
then Date.AddDays([Order Date],-1) else [Order Date])
,Day.Sunday) +1,Int64.Type),
(if (Date.DayOfWeek([Ship Date],Day.Sunday)+1) = 1
if (Date.DayOfWeek([Ship Date],Day.Sunday)+1) = 7
then Date.AddDays([Ship Date],-1) else [Ship Date])
,Day.Sunday) +1,Int64.Type),
#"Added Days Between" = Table.AddColumn(#"Added Ship Weekday", "Days Between Order and Ship", each if [Ship Date] is null then null else if [Order Date] is null then null else Duration.Days([Ship Date] - [Order Date]),Int64.Type),
#"Added Weekdays Between" = Table.AddColumn(#"Added Days Between", "Weekdays From Order to Ship Date", each if [Days Between Order and Ship] is null then null else
( if [Order Date Weekday] > [Ship Date Weekday] then (5 + [Ship Date Weekday] - [Order Date Weekday] ) else ( [Ship Date Weekday] - [Order Date Weekday] )) + (5 * (Number.RoundDown([Days Between Order and Ship]/7))),Int64.Type)
in