One of the most complicated changes in the new Tax Act passed in Dec 2017 was to the taxation of partners and shareholders in pass-through entities such as partnerships, LLC's and S Corps.
I have read many articles which just touch upon the 20% deduction in business income or go into so much depth that my head is spinning.
I found one article in the Journal of Accountancy that gives a setp by step guide to calculating the deduction: https://www.journalofaccountancy.com/issues/2018/may/sec-199a-deduction-for-qualified-business-income.html
Even so, there are still many moving parts. Thus, I created a summary of the article to help in my understanding of the nuances. I am sharing this with you. https://www.dropbox.com/s/1jovcqyzxrh4bt1/Sec%20199A%20QBI%20illustration.pdf?dl=0
While I am glad to talk you through this article and the pdf I created (please feel free to contact me), by no means am I an expert on this Sec. 199A law. I suggest you seek tax expertise for your particular situation.