PARALLELPERIODCalendarDate

PARALLELPERIOD is a Data Analysis Expressions (DAX) function used in Power BI, Excel Power Pivot, and SQL Server Analysis Services to shift the current date context by a specified number of time periods. It returns a table of dates that are parallel to the current period, allowing comparisons across time such as year-over-year or month-over-month analyses.

Syntax: PARALLELPERIOD(<dates>, <number_of_periods>, <interval>)

- <dates> is a column of date values that defines the calendar context, typically from a date dimension.

- <number_of_periods> is an integer indicating how many periods to shift; negative values move backward in time, positive values forward.

- <interval> is the time unit for the shift and can be YEAR, QUARTER, MONTH, or DAY.

How it works: PARALLELPERIOD produces a table of dates offset from the current filter context. It is commonly used inside CALCULATE to alter the date filter context so that a measure can be evaluated for a parallel time period, such as the same period in the previous year or the previous month.

Example: To compute total sales for the same period last year, you might use:

CALCULATE(SUM(Sales[Amount]), PARALLELPERIOD('Date'[Date], -1, YEAR))

Limitations and considerations: The function relies on a well-defined date dimension and proper relationships to the fact data. It operates best with continuous date tables and may be less intuitive in irregular calendars. It is one of several time-intelligence functions in DAX and can be used alongside DATEADD, PREVIOUSMONTH, or other period-shifting tools depending on the analysis needs.