New Tax Law Effect On Seniors Pension Income

AARP sent out an email saying I should check my withholding amount on pension income due to the new income levels and tax law changes. I tried the IRS calculator but I am confused. I have to pretend my pension income is a job so I did. If I include my SS income too I am way underpaying but not all my SS income is taxable. So do I just include the amount that was taxable last year, since it changes every year according to deductions, variable income, etc., which I guess are not longer allowable?

 

I figured it two different ways - once without SS income and I would be overpaying and once with it and I would be underpaying so I am hoping the real number is in between.

 

Has anyone figured this out?