I received a CP11 notice from the IRS stating that the tax computation for 2017 was incorrect and that I owed money.
What I don't understand is that my calculation (turbotax) and IRS's calculations are the same for AGI (line 37) and Taxable Income (line 43) but the Total Tax is different. Shouldn't Turbotax be able to calculate accurately that number? There are no other entries below line 43 or 63 that would have affected the tax calculation.
Line 37 is not the amount you're taxed on. That just determines what tax bracket you are in. The amount on line 43 is your taxable income that you're taxed on. Line 44 is your tax on that income. Is the IRS saying line 44 is wrong? Or some other line after tax payments and credits are taken into account?
For example, are you claiming to have already paid in more taxes through quarterly tax payments or W-2 withholding, yet the IRS says less was paid in?
Just found this, which may help you resolve this issue faster.
If you don't agree with the changes, contact the IRS within 60 days from the date of your notice. You can do this:
The tax due is calculated based on the kind of income in your return, not just simply the AGI or total taxable income. In your return, if you print all worksheets as well as the filed return, you may find a worksheet showing the tax calculation. If you look at your notice, it would appear the IRS is changing the methodology for the tax calculation based on a change in the type of income reported. It's typical that, if they change something in your return, they automatically change the tax calculation, often incorrectly so.