I show taxable income but zero tax owing?

[Critter]

That is very possible ... look at the return itself and see what is happening ...

You can peek at only  the Federal form 1040 and the summary of the state info by going here:

1) lower- Left side of the screen...click to the left side of the "Tax Tools" text selection.
2)  then select "Tools"
3) then select "View Tax Summary" from the pop-up
4) then back to the left-side and "Preview 1040"

Then hit the "Back" on the left side to get back to your tax entries.

To view your entire return using the online editions (including the state) before you file, you will need to pay for your online account.

To pay the TurboTax online account fees by credit card, without completing the 2018 return at this time, click on Tax Tools >>> Tools  and then Print Center.  Then click on Print, save or preview this year's return.  On the next page, to pay by credit card, click Continue.  On the next screen it will ask if you want Audit Defense, if you do not want this option just click on the Continue button.  The next screen will ask for all your credit card information so you can pay for the account.