For the tax on 1040 line 16? There may be credits that reduces the tax. Your total tax is on line 24.
There are like 7 different ways to calculate the tax.
It's very common for the tax to be less than you can figure using the IRS tables. It depends what kind of income you have. Even though the full amount shows up in the total income on the 1040 line 7, if you have capital gains or qualified dividends the tax 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 the worksheets to see it.