You are using the online Free Edition which only can run you through filing your 2016 taxes
The Desktop equivalent or so software package called Deluxe desktop @ $50 could provide you a means of doing a simulation. However, I don't understand your point at all about prepaying 2017 taxes.
Are you an employee and paid on only Form W-2?
Do you have any reason to believe that during the year your withholding will not be sufficient and you would need to file Estimated Tax Payments?
OK... I am starting this month as independent contractor. I learned I will need to start paying querterly taxes starting April 15th. I want to understand how and can I do it through Turbo Tax and how.
SuperUser Scruffy Curmudgeon brings up some good points.
If you decide you need to make quarterly estimated payments for 2017, TurboTax can assist you in calculating the quarterly estimated tax payments and will prepare vouchers (Form 1040-ES) for you to print. You cannot make the payments through TurboTax, however there are several options for making these payments.
To calculate estimated payments, please follow these steps:
1. Click on Federal Taxes > Other Tax Situations
2. On the screen, Let's check for any uncommon tax situations, in the Other Tax Forms section, click on the Start/Revisit box next to Form W-4 and Estimated Taxes.[See Screenshot #1, below.]
3. On the screen Adjust How Much Tax You Pay click the No box. [This is for withholding from a paycheck.]
4. On the next screen, Estimated Taxes for 2017, click the Prepare Now box. [Screenshot #2]
5. On the Review Your Estimates for 2017 screen TurboTax will display 2017 quarterly estimates based on your 2016 income. If you think your 2017 financial picture will differ, click on the Yes box to adjust your income or deductions. [Screenshot #3]
6. Continue through the screens, entering the requested information. TurboTax will then calculate your quarterly estimated payments for 2017.
Please see the following FAQ for great information about how making estimated payments to the IRS: https://ttlc.intuit.com/replies/3301891