Calculated fields are fields whose value is calculated on the fly instead of being stored in the Jira database. Their value is recalculated every time the issue is displayed or updated, or a re-index is performed. You can display calculated fields on issue and transition views, and you can use them in JQL searches such as in the Issue Navigator, Saved Filters, Agile Board queries, etc.

A calculated field can be a field that:

• Evaluates a Groovy expression to compute the value of the field based on other fields, other issues, versions, etc. The result can be a number, a date, a string, a duration, or a single- or multi-select option value.
• Returns the Date/Time of execution of one or more specified transitions of your workflow
• Returns the caller of one or more transitions of your workflow
• Returns the execution count of one or more transitions of your workflow
• Returns the status of the issue's parent, if any.
• Returns the Date/Time when a field was last modified
• Returns the user who last modified a field
• Etc.

Calculated fields provided by the add-on

The Jira Misc Custom Fields plugin provides a suite of custom fields for use in your custom JIRA workflows.