Tableau Error "Trend line cannot be computed" WIth the When you try to add trend lines to views, the following error might occur: A trend line cannot be computed. Typically, each axis should be either a number or a date. Refer to the Help for more information. To Fix the issue Right-click the date field on Rows or Columns, and select Continuous(usually date filed) as shown below. Now you can click on the mark(line or Bar) and select Trend Lines. You can see the trendline displayed.