Federal Tax Withholding Calculation

I'm retired and I get a monthly pension. I want to determine the  calculated amount of taxes to be withheld if I selecct  single or married filed jointly.  I don't have any dependents. The amount to be withheld will determine how much extra withholding I chose.

 

I can't find a calculator that will allow me to do this calculation. Depending on this calculation, I will revise my W-4P. Is there anything in turbotax that would do this calculation for a fixed monthly pension? If not, is there a website that would provide this?

 

Thank you.