TT is usually solid on core tax calculations - tax is not purely calculated based line 15 fed into the tax tables if that's what you are looking at; do you have any long term cap gains or qualified dividends, those are separated out and taxed at 0/15/20% depending in your situation, and the remaining income is put thru tax tables to derive line 16.
looks like you are using TT online which I am not as familiar with as desktop but if you are able to access PDF with "all forms and worksheets" look for the "Qualified Dividends and Capital Gain Tax Worksheet" which does the calculation for line 16. (if you are using desktop it's readily accessible throughout the tax prep process in Forms mode).
