SAMEPERIODLASTYEARDateDate

SAMEPERIODLASTYEAR is a DAX time intelligence function used in Power BI, SQL Server Analysis Services, and Excel data models. It returns a table of dates that corresponds to the same period in the previous year, based on the dates in the current filter context.

The function is commonly used to enable year-over-year comparisons for measures such as sales, revenue, or units. When placed inside a CALCULATE expression, SAMEPERIODLASTYEAR shifts the active date context one year back, allowing a measure to be evaluated for the same calendar period in the previous year.

Syntax and usage: SAMEPERIODLASTYEAR(<dates>) where <dates> is a date column from a date table or a column that represents a continuous date range. The function returns a single-column table of dates that align with the previous year for the dates currently filtered.

Example: Revenue LY = CALCULATE(SUM(Sales[Revenue]), SAMEPERIODLASTYEAR('Date'[Date]))

This computes total revenue for the same dates in the prior year, relative to the current calendar selection.

Requirements and considerations: A proper, continuous date table is required, and it must be related to the fact table containing the measures. The date table should be marked as a date table for correct behavior. Because SAMEPERIODLASTYEAR relies on calendar dates, it naturally handles leap years and varying month lengths. For fiscal calendars or non-standard periods, alternatives like PARALLELPERIOD or DATEADD with a custom date column may be more appropriate.

See also: PARALLELPERIOD, DATEADD, SAMEPERIODLASTMONTH, SAMEPERIODLASTQUARTER.