# Calculated fields and when to use parameters

*Tableau Desktop Foundations Study Guide · Exploring and Analyzing Data · Last updated October 29, 2026 · https://www.certifyforce.com/study-guide/tableau-desktop-foundations/exploring-and-analyzing-data/calculated-fields-and-when-to-use-parameters*

Write string, date and arithmetic calculated fields in the calculation editor (+ for concatenation, STR, DATEADD, DATEDIFF, DATEPART), know how a new calculated field lands in the Data pane, and decide when a parameter, a single workbook-wide value used in calculations, filters and reference lines, fits a requirement.

- Certification: Salesforce Tableau Desktop Foundations
- Exam section: Exploring and Analyzing Data
- Study guide: https://www.certifyforce.com/study-guide/tableau-desktop-foundations

**Official exam objective:**

> Apply analytics to a worksheet: Add a manual or a computed sort; Add a reference line; Use a quick table calculation; Use bins and histograms; Create a calculated field (for example, string, date, simple arithmetic); Explain when to use a parameter; Display totals on a worksheet.

## What the exam expects

- Create a calculated field from Analysis > Create Calculated Field and predict where it appears in the Data pane and how it aggregates.
- Write simple string calculations, converting numbers with STR before concatenating with +.
- Write date calculations with DATEADD, DATEDIFF and DATEPART and tell their return types apart.
- Write simple arithmetic calculations between measures.
- Explain when to use a parameter: a viewer-controlled value used in a calculation, a Top N filter or a reference line; create it, show its control, and know what deleting it breaks.

Key terms:
- **Calculated field:** a new field whose values come from a formula you write; saved to the Tableau data source, leaving the original data untouched.
- **Calculation editor:** the dialog where you name a calculated field and type its formula.
- **Type conversion (casting):** changing a value's data type inside a formula, such as STR to make a string.
- **Parameter:** a workbook variable, such as a number, date or string, that can replace a constant value in a calculation, filter or reference line.
- **Parameter control:** the worksheet card that lets viewers change a parameter's value.

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Create a calculated field | Analysis > Create Calculated Field | [Get Started with Calculations in Tableau](https://help.tableau.com/current/pro/desktop/en-us/calculations_calculatedfields_create.htm) |
| Numeric calculated field | Added to the Data pane as a measure | [Get Started with Calculations in Tableau](https://help.tableau.com/current/pro/desktop/en-us/calculations_calculatedfields_create.htm) |
| Calculated field icon | Equal sign (=) next to the data type icon | [Get Started with Calculations in Tableau](https://help.tableau.com/current/pro/desktop/en-us/calculations_calculatedfields_create.htm) |
| Default aggregation in a view | Automatically aggregated as a sum | [Get Started with Calculations in Tableau](https://help.tableau.com/current/pro/desktop/en-us/calculations_calculatedfields_create.htm) |
| Source data | Original data remains untouched | [Get Started with Calculations in Tableau](https://help.tableau.com/current/pro/desktop/en-us/calculations_calculatedfields_create.htm) |
| + operator | Adds numbers, concatenates strings | [Writing Calculations in Tableau](https://help.tableau.com/current/pro/desktop/en-us/functions_operators.htm) |
| STR | Casts its argument as a string | [Type Conversion](https://help.tableau.com/current/pro/desktop/en-us/functions_functions_typeconversion.htm) |
| DATEADD vs DATEDIFF | Returns a date vs returns an integer count | [Date Functions](https://help.tableau.com/current/pro/desktop/en-us/functions_functions_date.htm) |
| Parameter uses | Calculations, filters, reference lines | [Create Parameters](https://help.tableau.com/current/pro/desktop/en-us/parameters_create.htm) |
| Parameter scope | Global across the workbook | [Create Parameters](https://help.tableau.com/current/pro/desktop/en-us/parameters_create.htm) |
| Deleting a parameter | Calculated fields that use it become invalid | [Create Parameters](https://help.tableau.com/current/pro/desktop/en-us/parameters_create.htm) |

## Check yourself

- What three values must you specify when a parameter's allowable values are a Range?
- When can't a parameter use Range for its allowable values?
- Which date function returns an integer count of days between two dates?
- Why don't you re-add a calculated field to its view after editing its formula?

## Sources

- [Get Started with Calculations in Tableau](https://help.tableau.com/current/pro/desktop/en-us/calculations_calculatedfields_create.htm)
- [Writing Calculations in Tableau](https://help.tableau.com/current/pro/desktop/en-us/functions_operators.htm)
- [Type Conversion](https://help.tableau.com/current/pro/desktop/en-us/functions_functions_typeconversion.htm)
- [Date Functions](https://help.tableau.com/current/pro/desktop/en-us/functions_functions_date.htm)
- [Create Parameters](https://help.tableau.com/current/pro/desktop/en-us/parameters_create.htm)
- [Group Your Data](https://help.tableau.com/current/pro/desktop/en-us/sortgroup_groups_creating.htm)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 6 linked practice questions, and unlimited timed mock exams are included with the Tableau Desktop Foundations pack (USD $19): https://www.certifyforce.com/practice-exams