Taxable Roth conversion + backdoor Roth + Roth -> Traditional recharacterization after December 31 and form 8606

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I have a number of factors at play for my form 8606 and I'm concerned that the taxable amount (line 18) for my Roth conversion is too low for the 2023 tax year.

timeline:

2023 - $3,870 contribution to Roth IRA

2023 - $700 contribution to traditional IRA
2023 - Conversion from Traditional -> Roth of $1145 ($700 + $445 pretax dollars from a previous rollover)

2023 - Dec 31 traditional IRA balance is $89

2024 - $1,930 contribution to traditional IRA for 2023

2024 -  $5,427 re-characterization from Roth to Traditional ($3,870 + $1,557 in gains)

This is the resulting 8606:
1 - 6,500
2 - 0
3 - 6,500
4 - 1,930
5 - 4,570
6-12 are blank
13 - 1,145
14 - 5,355
16 -1,145
17 - 1,145
18 - 0

I'm questioning line 13. $1,145 out of $1,145 as non-taxable distributions seems incorrect (too high)

I'm expecting:

5 - 4,570

6 - 3,959 ($89 Dec 31 balance + $3,870 outstanding re-characterized contributions)

7 - 0

8 - 1,145

9 - 5,104

10 - 0.895

11 - 1024

12 - 0

13 - 1024

...
18 - 121

[ad2024 · Accepted solution]

I looked into this a bit further and it's related to the 2023 contribution that was made after Dec 31 + the equation of the 590b worksheet. What appears to be happening is that 8606's line 6 is calculated by omitting contributions made after Dec 31, but 590b's line 7 isn't. The effect this has is to defer taxes until next year (since having no taxable amount for this year reduces my IRA basis for next year)