I was thinking more about there assignment of the adjustments such as HSA deduction and carryover losses, I didn't have the latter but I had $4150 for HSA which I contributed in Q1. Which is similar problem to your 3k capital loss carryover, when to apply it if there are no offsetting gains. I found this article which explains why applying it all in Q1 can be problematic, because the annualization process is then effectively multiplying that 3 months worth of AGI including both income and deductions by 4, to come up with an annualized figure for that portion - which is fine on the income side, but it is multiplying your capital loss of 3k by 4 and effectively generates a 12k capital loss which wouldn't make sense. Similarly my HSA deduction should never exceed $4150 in each annualization.
https://www.taxact.com/support/986/2024/figuring-annualized-income-with-a-net-capital-loss?hideLayou...
Based on this it seems that for these type of deductions the best approach would be to allocate them proportionally for each period so the annualization never exceeds the limit of that deduction. For your HSA if you paid it in Q4 I don't know if it's ok to bring it forward proportionally, rather than just leave it in Q4 which is probably the most conservative approach.
It may also not matter. For my HSA I tried it both ways and the end result was the same because of the way the underpayment/overpayments in Q1-3 lined up with my uneven estimated taxes and I still owed $1.
This is outside of my expertise to advise one way or the other - I am just going thru the process myself but thought I'd share what I'd found.
