You can be very conservative and take what you owe now and divide by 12, and make extra payments of that amount, which would be $12,000 /12 or $1,000 more per month.

Or you can go to:

Other Tax Situations tab in TurboTax

then to Other Tax Forms

down to Form W-4 and Estimated Taxes and this will help project your overall taxes.

I prefer the first method, as you can have additional tax withheld from the retirement and then would not need to do estimated tax payments.  You may over withhold due the tax law changes for 2018, that is why I said conservative, but you would have no penalty.