For taxable income of $51,195 (married couple both over 65 and no dependents) Turbotax says I owe $5,717. But IRS tax tables show $5,753 is due and tax tables say $5,755?

[bryce_in_tx]

Normally I wouldn't question the software, but this year I have a small amount of foreign investment income that requires a Form 8621 be filed with the return.  I had to add the $12 of income to Turbotax manually.  It makes no difference in the tax I owe, it turns out.  But why the difference between Turbotax and the tax tables and tax rates?

[rjs]

The tax table is only one of seven different methods that can be used to calculate your tax, depending on what is in your tax return. Your tax return must require one of the other methods. The most common reason that you cannot use the tax table is that you have capital gains or qualified dividends.

In the IRS Instructions for Form 1040, look at the instructions for line 12a. Starting in the middle column on page 31 it explains the seven methods that can be used to calculate the tax on line 12a.

If you are looking at the Tax Rate Schedules in the IRS instructions, note that the Caution at the top says not to use the Tax Rate Schedules to calculate your tax.