where does Turbo Tax get the number in line 6 of Form 8606?

[mrwilliamylee]

the amount provided by TurboTax looks incorrect.

[baldietax]

8606 Line 6 is input by you, in the 1099-R section after inputting a 1099-R you get a summary of your 1099-Rs, hit Done/Continue and you will get a question about disaster then asks about basis carryover from 2024 (this question is also asked after Trad IRA contributions),  then asks you about MV of Trad IRAs as of 12/31/25:

[baldietax]

PS the onscreen guidance to use 5498s is misleading as those generally don't get sent til May.  Per IRS instructions for 8606 Line 6 use your year-end brokerage statements

[dmertz]

After you have entered your year-end balance as baldietax described, TurboTax stores this entry on line 18 of TurboTax's IRA Information Worksheet.