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:

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.