Common LOD use cases (customer first purchase, cohorts) in Tableau - Step-by-Step Guide

Introduction

Level of Detail (LOD) expressions in Tableau help you calculate values at different levels of detail than the view. This is useful when you want to find things like a customer's first purchase date or group customers into cohorts based on their first purchase.

When you want to find the first purchase date for each customer regardless of the current view filters.

When you need to create customer cohorts based on the month or year of their first purchase.

When you want to calculate metrics like retention or repeat purchases by cohort.

When you want to compare individual transactions to overall customer behavior.

When you want to fix a calculation at the customer level while showing data at a more detailed level.

Steps

Step 1: Open

- Tableau Desktop and connect to your data source

Your data appears in the Data pane

Step 2: Click

- Analysis menu > Create Calculated Field

A dialog box opens to create a new calculation

Step 3: Type

- Calculated Field dialog

You enter the LOD expression for first purchase date

💡 Use syntax like { FIXED [Customer ID] : MIN([Order Date]) } to get the first purchase date per customer

Step 4: Name

- Calculated Field dialog

You name the field 'Customer First Purchase Date'

💡 Choose clear names to remember what the calculation does

Step 5: Click

- OK button in Calculated Field dialog

The new calculated field appears in the Data pane

Step 6: Drag

- New calculated field to Rows or Columns shelf or Detail on Marks card

You see the first purchase date for each customer in your view

Step 7: Repeat

- Create Calculated Field dialog

You create cohort groups using a calculation like DATEPART('month', [Customer First Purchase Date])

💡 Use this to group customers by the month they made their first purchase

Before vs After

Before

View shows all orders with order dates and customer IDs but no summary of first purchase dates

After

View shows each customer with their first purchase date fixed, enabling cohort grouping and analysis

Settings Reference

FIXED LOD expression

📍 Calculated Field dialog

Calculates a value fixed at the specified dimension level regardless of view filters

Default: None

INCLUDE LOD expression

📍 Calculated Field dialog

Includes additional dimensions in the calculation beyond the view level

Default: None

EXCLUDE LOD expression

📍 Calculated Field dialog

Excludes specified dimensions from the calculation

Default: None

Common Mistakes

Using a regular aggregation like MIN([Order Date]) without FIXED LOD

This calculates the minimum date in the current view, which changes with filters and does not fix per customer

Use { FIXED [Customer ID] : MIN([Order Date]) } to get the first purchase date per customer regardless of filters

Creating cohorts without fixing the first purchase date

Cohorts will be inconsistent because the first purchase date changes with the view

Create a fixed LOD for first purchase date, then use that field to define cohorts

Summary

LOD expressions let you calculate values fixed at a specific level, like customer first purchase date.

Use FIXED LOD to get stable values regardless of filters or view level.

This helps create cohorts and analyze customer behavior over time.