Date calculations (DATEDIFF, DATEADD) in Tableau - Step-by-Step Guide

Introduction

Date calculations help you find differences between dates or add time to dates. This is useful when you want to see how much time passed or predict future dates in your data.

When you want to find how many days passed between order date and delivery date.

When you need to add 7 days to a start date to find a deadline.

When you want to compare sales month over month by adding or subtracting months.

When you want to calculate the number of years between a customer's signup date and today.

When you want to shift dates in your data to analyze trends over different time periods.

Steps

Step 1: Click

- Analysis menu

A dropdown menu appears with calculation options

Step 2: Select

- Create Calculated Field

A dialog box opens to enter a new calculation

Step 3: Type

- Calculation editor

You can write your date calculation formula

💡 Use DATEDIFF to find difference between two dates, e.g. DATEDIFF('day', [Start Date], [End Date])

Step 4: Type

- Calculation editor

You can write your date addition formula

💡 Use DATEADD to add time to a date, e.g. DATEADD('month', 1, [Order Date])

Step 5: Click

- OK button in the calculation editor

The new calculated field appears in the Data pane

Step 6: Drag

- New calculated field to Rows or Columns shelf

The visualization updates showing the date calculation results

Before vs After

Before

Data shows order dates and delivery dates as separate columns without any calculation

After

A new column shows the number of days between order and delivery for each record

Settings Reference

Date Part

📍 Inside DATEDIFF and DATEADD functions in calculation editor

Defines the unit of time to calculate difference or add (e.g., days, months)

Default: day

Start Date

📍 First date argument in DATEDIFF or DATEADD

The date to start calculation from

Default: None

End Date / Number

📍 Second date argument in DATEDIFF or number to add in DATEADD

The date to compare to or number of units to add

Default: None

Common Mistakes

Using DATEDIFF with wrong date part like 'days' instead of 'day'

Tableau requires exact date part keywords like 'day', not plural

Use correct date part keywords such as 'day', 'month', 'year' exactly as Tableau expects

Using DATEADD with a negative number but forgetting to put minus sign

Without minus sign, DATEADD adds time instead of subtracting

Use negative numbers to subtract time, e.g. DATEADD('month', -1, [Date])

Mixing date fields and non-date fields in calculations

DATEDIFF and DATEADD require date fields for correct results

Ensure both fields used are date type or convert text to date before calculation

Summary

DATEDIFF calculates the difference between two dates in units like days or months.

DATEADD adds or subtracts a specified number of time units to a date.

Use exact date part keywords and correct data types for accurate results.