I don't know any easy way to do it yourself...unless you had pure W-2 and interest income, SS and 1099-R income......because different calculation methods are used based upon what types of income are involved.
As soon as you start getting Dividends, or cap gains for for investments (these are most common), or rental income, or 1099-MISC/contractor/SE income...then a whole bunch of extra calculations can be involved.
Easiest step it to print out just your form 1040, and look at all the income and deduction/credit lines on that form to see if they look reasonable. Then TTX would likely have the right tax calculations.
An income line in lines 1-to-7 that seems to be waaayy off base, may indicate a mis-keyed or double entered income amount.
Line 16 shows a credit for what was supposedly withheld on your W-2 and various 1099-??? forms (usually 1099-R or SSA-1099) does that add up?
Other lines...depends on your situation, filing status, number of children and ages..
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
