I received a letter from the IRS asking how I calculated Line 8 of the schedule 2 form. I answer questions in Turbo tax. What would correspond to line 8 of this form?

[tagteam]

See https://www.irs.gov/instructions/i1040gi#en_US_2021_publink100020408

[VolvoGirl]

Schedule 2 line 8 is the 10% early withdrawal penalty from a IRA or 401K account  if you are under 59 1/2 or don't have an exception.  It's based on 1040 line 4b or 5b which comes from your 1099R.  

[dmertz]

Line 8 of Schedule 2 is for reporting an early-distribution penalty for a distribution from a retirement account (with or without Form 5329) or some other penalty calculated on Form 5329 (with Form 5329 included in your tax return).  As you said, TurboTax automatically populates Schedule 2 line 8 based on your entries of Forms 1099-R or your reporting of excess contributions or excess accumulations.  See the instructions for Form 5329:

https://www.irs.gov/pub/irs-pdf/i5329.pdf

If Form 5329 was included with your tax return, that would show the calculation(s) that resulted in the total that was included on Schedule 2 line 8.  If Form 5329 was not included and Schedule 2 line 8 was nonzero, that implies that your reported Forms 1099-R that that had code 1 in box 7 and did not require Form 5329 to show their sum because there was no other reason to file Form 5329.

[fanfare]

Perhaps you did not attach an explanation, which the IRS wants from you when you file that Form.

Explain what you did.

Include dates and amounts.

@beulah1