The IRS changed the underpayment penalty calculation and now it looks like I no longer owe a penalty. However, I've already filed. How do I get that portion back?

[fanfare]

if Turbotax changes your return afte you file you can hope that IRS corrects the error for you.

If not, you'll have to file an amended tax return.

Always print a copy of your completed tax return for your records, and review it carefully before e-Filing.

You will need it if you are audited by the IRS, or to amend because a TurboTax update changes your return.