Velocity chart

[Sura Al-Jailawi]

Hello, 

I am new Scrum master and new in Jira also 

I am trying to make a good prediction of tasks during a Sprint for my team and I want to use the old sprint to make a realistic prediction. 

My question is if the calculation the velocity chart depending on the Story points number why jira doesn't cosider sub-tasks in the equations and put the Story (task type) to equal to 0 

Isn't that make the velocity chart not so accurate? 

[Nic Brough -Adaptavist-]

Sub-tasks are not sprint-able items, they are a part of stories (which are).  You don't commit to sub-tasks, you commit to doing the stories, and estimates measure commitment vs delivery.

There are a number of ways of doing estimates on sub-tasks, but Jira has taken the simple route and does not support them at all.  In off-the-shelf Jira, don't put estimates on sub-tasks (or if you do, educate your users that they're nothing to do with your sprint velocity or progress)