After you file

Yes you will need to file a 1040X if the information on the K-1 affects reportable income.  Or, you can choose to file for an extension to file your 1040.

All form K-1s are not due until March 15th. If the Sub S corporation files an extension however, then the K-1 does not have to be issued until September 15th.  This April 15th due date makes it very challenging for taxpayers. Their individual income tax return is due the same day. You can’t file your individual income tax return without your K-1s.

The 2021 individual income tax return, Form 1040, is due on April 15, 2022. If you can’t file on time because you did not receive your K-1 timely, you will need to file an extension. This is done on Form 2848, Application for Automatic Extension of  Time to File U.S. Income Tax Return. A properly filed extension request will extend the due date to file until October 15, 2021. The extension only extends the time to file the return. It does not extend the time to pay any tax due. Any tax due needs to be paid by April 15th. Failure to pay the tax then will result in interest and penalty.

Have I confused you?  Well, the short story is you can file now and be prepared to amend when you receive your K-1 or you can file an extension on your form 1040.

If you decide to extend - Follow these steps to file for an extension using Turbotax:  Filing an Extension Using TurboTax

IRS extensions for tax year 2021 must be filed on or before April 18, 2022 for domestic taxpayers.

It isn't possible to file a post-deadline extension.

Keep in mind: An extension doesn't give you extra time to pay your taxes — but it will keep you from getting a late filing penalty. (You'll still owe interest if you pay after the deadline).

1. Open your return in TurboTax Online.
   (To do this, sign in to TurboTax and select Pick up where you left off).
2. Select File an extension at the bottom of the column on the left side of the screen.
   • If you don't see the File an extension button in Step 2 above, search for extend using your product's search function and select the Jump to link at the top of your search results.
3. Follow the on-screen instructions to e-file your extension.

Note: If you're paying additional taxes owed with direct debit, you'll need to provide your 2020 AGI for verification purposes (if you didn't file a 2020 return, enter 0 as your AGI).

If you don't have your AGI, or your extension gets rejected for the wrong AGI, here are 2 options:

1. Recommended: Pay your taxes at IRS Direct Pay (this also automatically gives you an extension).
2. Download and print Form 4868, fill it out, and get it postmarked before 11:59 p.m. on April 18. Payment and mailing instructions are on pages 3 and 4 of your printout.