SAMEPERIODLASTYEAR in Power BI - Dashboard Guide

Dashboard Mode - SAMEPERIODLASTYEAR

Business Question

How did our monthly sales perform this year compared to the same months last year?

Sample Data

Month	Year	Sales
January	2023	1000
February	2023	1200
March	2023	1500
January	2022	900
February	2022	1100
March	2022	1300

Dashboard Components

• KPI Card: Total Sales This Year
  Formula: Total Sales = CALCULATE(SUM(SalesData[Sales]), SalesData[Year] = 2023)
  Result: 3700
• KPI Card: Total Sales Last Year
  Formula: Sales LY = CALCULATE(SUM(SalesData[Sales]), SAMEPERIODLASTYEAR(SalesData[Date]))
  Result: 3300
• Line Chart: Monthly Sales Comparison
  X-axis: Month
  Y-axis: Sales
  Series: This Year and Last Year
  Measures:
  Sales This Year = CALCULATE(SUM(SalesData[Sales]), SalesData[Year] = 2023)
Sales Last Year = CALCULATE(SUM(SalesData[Sales]), SAMEPERIODLASTYEAR(SalesData[Date]))
• Table: Sales by Month and Year
  Columns: Month, Year, Sales

Dashboard Layout

+----------------------+----------------------+
| Total Sales This Year | Total Sales Last Year |
+----------------------+----------------------+
|                      Line Chart               |
|          Monthly Sales Comparison              |
+-----------------------------------------------+
|                 Sales by Month Table           |
+-----------------------------------------------+

Interactivity

A slicer for Year allows users to select 2023 or 2022. When the year changes, the KPI cards and line chart update to show sales for the selected year and the same period last year. The table filters to show only data for the selected year.

Self Check

If you add a filter selecting only February, which components update and what sales values do they show?

• KPI Cards: Show sales for February 2023 (1200) and February 2022 (1100).
• Line Chart: Shows only February points for both years.
• Table: Shows only February rows for both years.

Key Result

Dashboard compares monthly sales this year to the same months last year using SAMEPERIODLASTYEAR.

Practice

1. What is the main purpose of the SAMEPERIODLASTYEAR function in Power BI?

easy

A. To calculate the total sales for the current year

B. To compare data from the same period in the previous year

C. To filter data for the current month only

D. To create a new date column with next year's dates

Solution

1. Step 1: Understand the function's purpose

   SAMEPERIODLASTYEAR shifts the date context back exactly one year to compare the same time periods.

2. Step 2: Identify the correct use case

   It is used to compare measures like sales or revenue from this year to the same period last year.

3. Final Answer:

   To compare data from the same period in the previous year -> Option B

4. Quick Check:

   SAMEPERIODLASTYEAR compares last year's period [OK]

Hint: Think "same time last year" for comparison [OK]

Common Mistakes:

• Confusing it with total aggregation functions
• Using it to filter current year data
• Assuming it creates future dates

2. Which of the following is the correct syntax to use SAMEPERIODLASTYEAR with a date column named Sales[Date]?

easy

A. SAMEPERIODLASTYEAR('Sales'[Date])

B. SAMEPERIODLASTYEAR(Sales[Date])

C. SAMEPERIODLASTYEAR(Sales.Date)

D. SAMEPERIODLASTYEAR([SalesDate])

Solution

1. Step 1: Recognize correct table and column reference

   In DAX, table and column names are referenced as 'TableName'[ColumnName], so 'Sales'[Date] is correct.

2. Step 2: Check syntax correctness

   SAMEPERIODLASTYEAR(Sales[Date]) omits single quotes around the table name. SAMEPERIODLASTYEAR(Sales.Date) uses invalid dot notation. SAMEPERIODLASTYEAR([SalesDate]) uses an incorrect column name format.

3. Final Answer:

   SAMEPERIODLASTYEAR('Sales'[Date]) -> Option A

4. Quick Check:

   Correct DAX column reference uses quotes and brackets [OK]

Hint: Use single quotes for table, brackets for column [OK]

Common Mistakes:

• Omitting single quotes around table name
• Using dot notation instead of brackets
• Referencing columns without table name

3. Given the measure:

Sales LY = CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date]))

If total sales for March 2023 are 1000, and for March 2022 are 800, what will Sales LY show when filtered on March 2023?

medium

A. 800

B. 1800

C. 1000

D. 0

Solution

1. Step 1: Understand the measure calculation

   The measure sums sales amounts but shifts the date filter to the same period last year using SAMEPERIODLASTYEAR.

2. Step 2: Apply the filter context for March 2023

   When filtered on March 2023, the measure returns sales from March 2022, which is 800.

3. Final Answer:

   800 -> Option A

4. Quick Check:

   Sales LY shows last year's same period sales [OK]

Hint: SAMEPERIODLASTYEAR shifts filter to last year [OK]

Common Mistakes:

• Assuming it sums current year sales
• Adding current and last year sales
• Returning zero if no explicit filter

4. You wrote this measure:

Sales LY = CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR(Sales[Date]))

But it returns an error. What is the likely cause?

medium

A. Measure name cannot contain spaces

B. SUM function cannot be used inside CALCULATE

C. SAMEPERIODLASTYEAR requires a numeric column

D. Missing single quotes around the table name 'Sales'

Solution

1. Step 1: Check table and column references

   The table name 'Sales' must be enclosed in single quotes when referenced in DAX, so Sales[Date] is invalid.

2. Step 2: Understand function requirements

   SUM inside CALCULATE is valid, SAMEPERIODLASTYEAR requires a date column, and measure names can have spaces.

3. Final Answer:

   Missing single quotes around the table name 'Sales' -> Option D

4. Quick Check:

   Table names need single quotes in DAX [OK]

Hint: Always quote table names in DAX formulas [OK]

Common Mistakes:

• Forgetting single quotes around table names
• Thinking SUM can't be inside CALCULATE
• Assuming SAMEPERIODLASTYEAR needs numeric columns

5. You want to create a measure that shows the percentage change in sales compared to the same period last year. Which DAX formula correctly uses SAMEPERIODLASTYEAR to calculate this?

hard

A. Sales YoY % = CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date])) - SUM('Sales'[Amount])

B. Sales YoY % = SUM('Sales'[Amount]) / SAMEPERIODLASTYEAR('Sales'[Date])

C. Sales YoY % = DIVIDE(SUM('Sales'[Amount]) - CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date])), CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date])))

D. Sales YoY % = SUM('Sales'[Amount]) - CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date]))

Solution

1. Step 1: Understand the percentage change formula

   Percentage change = (Current - Previous) / Previous, so we need current sales minus last year's sales divided by last year's sales.

2. Step 2: Analyze each option

   Sales YoY % = DIVIDE(SUM('Sales'[Amount]) - CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date])), CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date]))) correctly uses DIVIDE to avoid errors and calculates the difference over last year's sales. Sales YoY % = SUM('Sales'[Amount]) / SAMEPERIODLASTYEAR('Sales'[Date]) divides sales by a date column, which is invalid. Sales YoY % = CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date])) - SUM('Sales'[Amount]) subtracts current from last year without division. Sales YoY % = SUM('Sales'[Amount]) - CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date])) calculates difference but not percentage.

3. Final Answer:

   Sales YoY % = DIVIDE(SUM('Sales'[Amount]) - CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date])), CALCULATE(SUM('Sales'[Amount]), SAMEPERIODLASTYEAR('Sales'[Date]))) -> Option C

4. Quick Check:

   Percentage change = (Current - LastYear) / LastYear [OK]

Hint: Use DIVIDE for safe percentage calculations [OK]

Common Mistakes:

• Dividing by a date column instead of sales
• Forgetting to divide difference by last year's sales
• Subtracting without calculating percentage