TurboTax Amendment Showing Incorrect Tax Due Before Changes — Why?

Dear all,

I’m looking for help understanding an issue while amending my 2025 tax return in TurboTax.

My original return shows a $3,978 refund.

However, I realized I forgot to include a 1099-B for stock sales (long-term), totaling about $3,000 in capital gains. Based on this, I would still expect to receive a reduced refund after amending — not owe taxes.

Here are the exact steps I followed:

1. How do I amend my return? → Start an amendment
2. Why are you amending? → Adding or updating a tax form → My form isn’t listed
3. TurboTax states: “We’re going to change the refund monitor to $0 to show the difference between your original and amended return.”
4. I land on “Here’s the info for your amended federal return”
5. I go to:
   Wages & Income → Stocks, Cryptocurrency, Mutual Funds, Bonds → Edit

At this point, before I even add anything:

• The top-left numbers suddenly change to:
  Federal due: $1,370
  CA due: $540

This is very confusing because:

• I haven’t added my missing 1099-B yet
• I expected the refund monitor to show $0 initially (as TurboTax explained)
• Instead, it immediately shows that I owe money, and I don’t understand how these numbers are calculated

I then proceeded to enter my 1099-B (~$3k capital gain), and at the end TurboTax still shows that I owe these amounts, which doesn’t seem correct given my original refund.

I’ve been stuck on this for a while and can’t figure out what’s happening.

This is a link to a quick screen recording of the process I followed for clarity.

Questions:

• Why does TurboTax show a tax due immediately when starting an amendment?
• What do these “Federal due” and “CA due” numbers represent at that stage?
• Are these real amounts owed, or just interim calculations?

Any guidance would be greatly appreciated.

Thanks in advance.