Trend analysis in Tableau - Cell-by-Cell Formula Trace

Sample Data

Monthly sales data for five months

Cell	Value
A1	Month
B1	Sales
A2	Jan
B2	100
A3	Feb
B3	120
A4	Mar
B4	130
A5	Apr
B5	150
A6	May
B6	170

Formula Trace

TREND(Sales)

Step 1: Identify sales values: [100, 120, 130, 150, 170]

Step 2: Assign time index to months: [1, 2, 3, 4, 5]

Step 3: Calculate slope (m) of trend line using formula: m = (N*Σxy - Σx*Σy) / (N*Σx² - (Σx)²)

Step 4: Calculate intercept (b) using formula: b = (Σy - m*Σx) / N

Step 5: Calculate trend values for each month: y = m*x + b

Cell Reference Map

    A      B
1 Month  Sales
2 Jan    100
3 Feb    120
4 Mar    130
5 Apr    150
6 May    170

Arrows: Sales values from B2:B6 feed into TREND calculation

Sales values from cells B2 to B6 are used to calculate the trend line.

Result

    A      B       C
1 Month  Sales   Trend
2 Jan    100     41
3 Feb    120     58
4 Mar    130     75
5 Apr    150     92
6 May    170     109

Column C shows the trend line values calculated for each month, indicating the sales trend.

Sheet Trace Quiz - 3 Questions

What is the slope of the trend line calculated from the sales data?

A 92.5

B 17

C 150

D 670

Key Result

TREND fits a straight line to data points by calculating slope and intercept to predict values over time.