Difference and percent difference in Tableau - Dashboard Guide

Dashboard Mode - Difference and percent difference

Business Question

How have sales changed from the previous month? Show both the difference and the percent difference.

Sample Data

Month	Sales
January	1000
February	1200
March	900
April	1500
May	1300
June	1600

Dashboard Components

• KPI Card: Total Sales Current Month
  Formula: SUM([Sales]) filtered by selected month
  Example: For April, shows 1500
• KPI Card: Difference from Previous Month
  Formula: SUM([Sales]) - LOOKUP(SUM([Sales]), -1)
  Example: For April, 1500 - 900 = 600
• KPI Card: Percent Difference from Previous Month
  Formula: (SUM([Sales]) - LOOKUP(SUM([Sales]), -1)) / LOOKUP(SUM([Sales]), -1)
  Example: For April, (1500 - 900) / 900 = 0.6667 (66.67%)
• Line Chart: Sales Over Months
  X-axis: Month
  Y-axis: Sales
  Shows trend of sales month to month
• Table: Monthly Sales with Difference and Percent Difference
  Columns: Month, Sales, Difference, Percent Difference
  Uses same formulas as KPI cards but for all months
  First month difference and percent difference show as blank or 0

Dashboard Layout

+--------------------------------------------------+
| Total Sales Current Month | Difference | % Diff  |
|        [KPI Card]         | [KPI Card] | [KPI]   |
+--------------------------------------------------+
|                                                  |
|               Sales Over Months                   |
|                 [Line Chart]                      |
|                                                  |
+--------------------------------------------------+
|                                                  |
|    Monthly Sales Table with Difference Columns   |
|                 [Data Table]                      |
|                                                  |
+--------------------------------------------------+

Interactivity

User selects a month from a filter dropdown. The KPI cards update to show sales, difference, and percent difference for that month. The line chart highlights the selected month. The table shows all months with their sales and differences, but the selected month is emphasized.

Self Check

If you add a filter to select the month "May", which components update and what values do they show?

• KPI Cards update to May sales (1300), difference (1300 - 1500 = -200), and percent difference (-200 / 1500 = -13.33%)
• Line chart highlights May
• Table remains showing all months but highlights May row

Key Result

Dashboard shows monthly sales with difference and percent difference from previous month using KPI cards, line chart, and table.

Practice

1. What does the Difference calculation in Tableau typically show?

easy

A. The total sum of all values

B. The average value over time

C. How much a value changed between two points

D. The maximum value in a dataset

Solution

1. Step 1: Understand the meaning of Difference

   Difference measures the change in value from one point to another, showing increase or decrease.

2. Step 2: Compare with other options

   Sum, average, and maximum describe different calculations unrelated to change between points.

3. Final Answer:

   How much a value changed between two points -> Option C

4. Quick Check:

   Difference = Change amount [OK]

Hint: Difference = New value minus old value [OK]

Common Mistakes:

• Confusing difference with total sum
• Thinking difference shows average
• Mixing difference with maximum value

2. Which of the following Tableau calculations correctly computes the percent difference between the current and previous value?

easy

A. ([Current Value] - [Previous Value]) / [Previous Value]

B. ([Previous Value] - [Current Value]) / [Current Value]

C. [Current Value] + [Previous Value] / [Previous Value]

D. [Current Value] * [Previous Value]

Solution

1. Step 1: Recall percent difference formula

   Percent difference = (New - Old) / Old, showing change relative to original.

2. Step 2: Match formula to options

   ([Current Value] - [Previous Value]) / [Previous Value] matches formula exactly; others either reverse or misuse operations.

3. Final Answer:

   ([Current Value] - [Previous Value]) / [Previous Value] -> Option A

4. Quick Check:

   Percent difference = (New - Old) / Old [OK]

Hint: Percent difference = difference divided by previous value [OK]

Common Mistakes:

• Swapping numerator terms
• Dividing by current value instead of previous
• Using addition or multiplication instead of division

3. Given this Tableau calculated field:
LOOKUP(SUM([Sales]), 0) - LOOKUP(SUM([Sales]), -1)
What does this calculation return?

medium

A. The percent difference in sales between current and previous row

B. The total sales for all rows

C. The sum of sales for the previous row only

D. The difference in sales between the current and previous row

Solution

1. Step 1: Understand LOOKUP function usage

   LOOKUP(SUM([Sales]), 0) returns current row sales; LOOKUP(SUM([Sales]), -1) returns previous row sales.

2. Step 2: Calculate difference

   Subtracting previous from current gives the difference in sales between rows.

3. Final Answer:

   The difference in sales between the current and previous row -> Option D

4. Quick Check:

   LOOKUP difference = sales change [OK]

Hint: LOOKUP with offset -1 gets previous row value [OK]

Common Mistakes:

• Thinking it calculates percent difference
• Assuming it sums all sales
• Confusing current and previous row values

4. You wrote this Tableau formula to calculate percent difference:
(SUM([Sales]) - LOOKUP(SUM([Sales]), -1)) / SUM([Sales])
But the results seem incorrect. What is the likely error?

medium

A. Not using WINDOW_SUM instead of SUM

B. Dividing by current sales instead of previous sales

C. Subtracting current sales from previous sales

D. Using LOOKUP with offset -1 incorrectly

Solution

1. Step 1: Analyze denominator in formula

   The formula divides by SUM([Sales]) which is current sales, but percent difference should divide by previous sales.

2. Step 2: Identify correct denominator

   Correct formula divides by LOOKUP(SUM([Sales]), -1) to get previous sales as denominator.

3. Final Answer:

   Dividing by current sales instead of previous sales -> Option B

4. Quick Check:

   Percent difference denominator = previous value [OK]

Hint: Divide by previous value, not current, for percent difference [OK]

Common Mistakes:

• Using current value as denominator
• Confusing subtraction order
• Misusing LOOKUP offset

5. You want to create a Tableau dashboard showing monthly sales percent difference compared to the previous month. Which approach correctly calculates this and handles months with zero sales without errors?

hard

A. Use (SUM([Sales]) - LOOKUP(SUM([Sales]), -1)) / NULLIF(LOOKUP(SUM([Sales]), -1), 0) to avoid division by zero

B. Use (SUM([Sales]) - LOOKUP(SUM([Sales]), -1)) / SUM([Sales]) ignoring zero sales

C. Use SUM([Sales]) / LOOKUP(SUM([Sales]), -1) without subtraction

D. Use WINDOW_SUM(SUM([Sales])) - WINDOW_SUM(SUM([Sales])) for difference

Solution

1. Step 1: Calculate percent difference with zero check

   Percent difference = (Current - Previous) / Previous; use NULLIF to avoid division by zero errors when previous sales are zero.

2. Step 2: Evaluate options for correctness

   Use (SUM([Sales]) - LOOKUP(SUM([Sales]), -1)) / NULLIF(LOOKUP(SUM([Sales]), -1), 0) to avoid division by zero uses NULLIF to prevent errors; others either divide by current or ignore zero sales causing errors or wrong results.

3. Final Answer:

   Use (SUM([Sales]) - LOOKUP(SUM([Sales]), -1)) / NULLIF(LOOKUP(SUM([Sales]), -1), 0) to avoid division by zero -> Option A

4. Quick Check:

   Use NULLIF to handle zero denominator [OK]

Hint: Use NULLIF to prevent division by zero in percent difference [OK]

Common Mistakes:

• Dividing by current sales instead of previous
• Ignoring zero sales causing errors
• Using sum differences without percent calculation