If you filed with Turbotax online, in some cases the housing allowance was not reported. To verify this, you would need to look at schedule SE line 2 and compare it to form 1040 line 7. Schedule SE line 2 should be more than line 7 by the amount of the allowance.
To file an amended return, see the instructions below. You will need to download a copy of Turbotax to install on your own computer. You also need to download your tax data file from your online account. Before you start the amended return, save a backup copy of your tax data file. Open the tax data file and click the forms icon to change to forms mode, and either save all forms and worksheets, or at least print or make pdfs of schedule SE and the Schedule SE Adjustment worksheet. Also print out and save copies of posts from this board documenting the bug (evidence for later).
Then prepare your amended return, print and sign it, and mail it to the IRS. Use a postal service with tracking numbers. Don't pay a penalty or accept turbotax's offer to calculate the penalty for you.
The IRS will probably send you a bill for a late penalty plus interest in a few months.
If this is your first ever penalty, you could request an abatement from the IRS. However, the interest is still owed and can't be waived or abated.
However, you can also make a claim under the Accuracy Guarantee, also attached below. You must make the claim within 30 days of receiving the penalty notice. Turbotax is supposed to cover your late fees and interest (but not the tax) assuming they agree this was their mistake. That's why you need to keep copies of the board posts as evidence.
(In the event that Turbotax claims this is user error, you can request an abatement from the IRS. Do this even if you continue to fight Turbotax, so that the penalty doesn't continue to grow over time.)
Amend https://ttlc.intuit.com/replies/3288565
https://ttlc.intuit.com/replies/4202723
