It depends on what kind of income you have, if you have capital gains or qualified dividends the tax on line 12 is not taken from the tax table but is calculated separately from schedule D. The tax will be calculated on the Qualified Dividends and Capital Gain Tax Worksheet. It does not get filed with your return. In the online version you need to save your return as a pdf file and include all worksheets to see it.
For the Desktop version you can switch to Forms Mode and open the worksheet to see it. Click Forms in the upper right (upper left for Mac) and look through the list and open the Qualified Dividends and Capital Gain Tax Worksheet.
You can probably tell because the tax on 1040 line 12a will be less than the Tax Table
Did you enter any qualified dividends or had capital gains entered? If so, the tax tables are not used to calculate your tax liability. The Qualified Dividends and Capital Gains Worksheet is used - https://www.irs.gov/pub/irs-pdf/i1040gi.pdf#page=33