Comprehensive Detailed Explanation

Requirement

We have two columns in Power Query Editor:

Order_Date

Shipping_Date

We need to calculate the number of days between the two dates.

Step 1: How date differences work in Power Query (M language)

Subtracting two date or datetime values in Power Query returns a duration value.

Example:

[Shipping_Date] - [Order_Date]

This produces a duration such as 3.00:00:00 (3 days).

Step 2: Converting duration into days

To get the number of days as an integer, we use Duration.Days().

Example:

Duration.Days([Shipping_Date] - [Order_Date] )

This returns 3 if the shipping date is 3 days after the order date.

Step 3: Evaluate other options

A. Duration.From → Converts a value to a duration type but does not extract the number of days.

B. Date.AddDays → Adds days to a given date, not used for calculating the difference.

C. Duration.Days → Correct, extracts total days from a duration.

D. DateTime.LocalNow → Returns the current system datetime, unrelated to this requirement.

References

Duration.Days function (Power Query M)

Working with dates in Power Query