Related issues for the Calculated Field post function can be identified by one of the following Jira concepts:
Issue link: You can define the link type to define which issues will be modified by the operation. If the post function includes the link type is ANY option, the operation will be performed on any linked issues.
Parent / Sub-Task: The related issue is either a parent or a subtask of the issue.
Epic / Issue inEpic: The other issue is either an epic related by an epic link or it is part of an epic. This is only applicable if you have Jira Software installed.
JQL: A JQL query will be executed to retrieve the issues the post function will modify. You can use some placeholders in the JQL query, which will be replaced with the current field values of the issue in transition. For tips on writing the JQL query, see JQL Reference or our JQL Use Cases for some examples.
To define your formula, select the field on which the calculated value will be set, then enter your desired formula. You can select other fields, numbers, and mathematical expressions to calculate the formula. For example, you can select Total story points to display the sum of story points for all the issues in an epic. See Calculated Field formulas for more information.