(#1#) If, during 2023 (including the January 15, 2024 payment) you pay in 100% (or more) of your 2022 taxes, then you are OK as far as estimated tax underpayment interest and penalty, no matter how high your 2023 income ends up being.
(#2#) The other safe harbor is paying 90% (or more) of your 2023 taxes during 2023 (including the January 15, 2024 payment)
Myself, I'm using the first safe harbor so I don't have to worry, as my estimated tax payments in 2023 (and Jan 15 2024) are already paid or auto-scheduled to be paid.
In a year when I use the 2nd safe harbor, as I do in some years, then yes, it sucks when I get a surprise extra income or extra "income" (quotes on the latter "income" when I do a Roth conversion or an IRA withdrawal larger than I had planned). Fortunately the surprises are mostly in December, so I have time to make a larger payment Jan 15 of the following month.
My income also varies quite a bit with dividends which are somewhat unpredictable... I just assume I'm going to get about 10% more dividends than the previous year, which is almost always an overestimate.
If I do sell something subject to capital gains tax, then, yup, I have to re-estimate estimated taxes if I'm using the 2nd safe harbor.
I'm not going to get any Minnesota tax rebate check because I had a bit more income and "income" than the limit, so I don't have that "surprise".
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