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.
To check withholding on line 17 you need to go back and check each W2 box 2 and 1099 box 4. Is line 17 too much or too little? What kind of 1099? Do you get any Social Security? You can have withholding on that.
