Yes. You should include a copy of your Form 1099-B to both Federal and State.
Because you summarized, the IRS and the California Franchise Tax Board (FTB) need the supporting data to match your numbers.
Note: You can just print the summarized pages and the detailed transaction pages from your brokerage 1099-B and staple them to the back of your amended return.
Yes. It is recommended that you submit Form 843. If you have had a clean record for the three years prior to 2024, the IRS will almost always wipe the "Failure to Pay" or "Failure to File" penalties for a first-time oversight.
However, do not file Form 843 with your amendment. Wait until the IRS processes your amendment and sends you a bill (notice) for the interest and penalties.
because the IRS systems need to "charge" the penalty before they can "abate" it.
Once you get that bill, you can often just call the IRS and ask for a "First-Time Abatement" over the phone, which is much faster than mailing Form 843.
Summary checklist for mailing:
- Federal: Send Form 1040-X + a copy of your 1099-B + any changed schedules (like Schedule D)
- State: Send Form 540-X + a copy of your 1099-B
- Payment: If you owe money, include a check or pay online via the IRS/FTB websites. Paying immediately stops interest from growing
- Tracking: Send both via Certified Mail with a return receipt. This is your only proof that you met the deadline if the mail gets lost
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