# PARALLELPERIOD Function (DAX)

**SQL Server 2008 R2**

Returns a table that contains a column of dates that represents a period parallel to the dates in the specified dates column, in the current context, with the dates shifted a number of intervals either forward in time or back in time.

This function takes the current set of dates in the column specified by dates, shifts the first date and the last date the specified number of intervals, and then returns all contiguous dates between the two shifted dates. If the interval is a partial range of month, quarter, or year then any partial months in the result are also filled out to complete the entire interval.

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To understand more about how context affects the results of formulas, see Context in DAX Formulas. |

The dates argument can be any of the following:

A reference to a date/time column,

A table expression that returns a single column of date/time values,

A Boolean expression that defines a single-column table of date/time values.

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Constraints on Boolean expressions are described in the topic, CALCULATE Function (DAX). |

If the number specified for number_of_intervals is positive, the dates in dates are moved forward in time; if the number is negative, the dates in dates are shifted back in time.

The interval parameter is an enumeration, not a set of strings; therefore values should not be enclosed in quotation marks. Also, the values: year, quarter, month should be spelled in full when using them.

The result table includes only dates that appear in the values of the underlying table column.

The PARALLELPERIOD function is similar to the DATEADD function except that PARALLELPERIOD always returns full periods at the given granularity level instead of the partial periods that DATEADD returns. For example, if you have a selection of dates that starts at June 10 and finishes at June 21 of the same year, and you want to shift that selection forward by one month then the PARALLELPERIOD function will return all dates from the next month (July 1 to July 31); however, if DATEADD is used instead, then the result will include only dates from July 10 to July 21.

If the dates in the current context do not form a contiguous interval, the function returns an error.

The following sample formula creates a measure that calculates the previous year sales for Internet sales.

To see how this works, create a PivotTable and add the fields, CalendarYear and CalendarQuarter, to the Row Labels area of the PivotTable. Then add a measure, named Previous Year Sales, using the formula defined in the code section, to the Values area of the PivotTable.

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The above example uses the table DateTime from the DAX sample workbook. For more information about samples, see Get Sample Data for PowerPivot . |

=CALCULATE(SUM(InternetSales_USD[SalesAmount_USD]), PARALLELPERIOD(DateTime[DateKey],-1,year))