Is there a product to calculate estimated tax payments during the year as portfolio income changes?

[LinaJ2018]

Yes, there is.  You can simply use the Tax Caster calculator.  Click here  TaxCaster .  You can even download the app and access it anytime anywhere.  However, as of today, it is using the 2018 tables and laws to calculate. If you want to know the 2019 figures, what you are seeing might not be accurate.   When there is an amendment in the regulations in the future, the program will get updated later. 

Or 

You can simply use the IRS withholding calculator for 2019 IRS withholding calculator.