Get your taxes done using TurboTax

Yes and yes. You should file Form 1040X, as well as an amended California return to amend your prior year returns and properly report the discrepancy. 

If you used TurboTax last year, you can locate your prior year documents and returns by scrolling to the bottom of your Tax Home screen.

Since they were all long-term, you will not need to re-enter all of the sales. You can simply input the amount of the discrepancy when you are in the Investment Income section in the Federal Wages & Income category.

Here are the steps within TurboTax:

1. Open the tax year you need to change
2. Start the Federal Amendment first. Navigate to Wages & Income, Investment Income, Stocks, Cryptocurrency, Mutual Funds, Other
3. Edit the existing entry 
4. Enter the correct Form 1099-B information. TurboTax will compare this to what you did previously and generate the Form 1040-X automatically.
5. Review the State Section. After finishing Federal, go to the State tab to ensure the California amendment is triggered.

Note that you will need to mail these documents along with your amended returns:

Federal:

1. Form 1040-X: The main amendment form, signed and dated.
2. Corrected Forms/Schedules: Updated Schedule D and Form 8949
3. Form 1099-B: Highly recommended to include a copy of the new Form 1099-B for quick verification by IRS
4. Payment: Since the new Form 1099-B shows that you owe more tax, include a check or money order payable to "United States Treasury." Write your SSN and "2025 Form 1040-X" on the memo line.

California:

1. Form 540 (Amended): In California, you typically file a new Form 540 with the "Amended" box checked at the top
2. Schedule X: This is the California-specific form used to explain the changes
3. Copy of Federal 1040-X: California requires a complete copy of your federal amended return to be attached to your state amendment
4. Form 1099-B: Include a copy for the State