I'm self employed and my income tends to be pretty volatile, but every year so far it has increased since I started paying taxes. For example, it increased substantially from 2021 to 2022, so for my quarterly 2022 tax payments, I was able to avoid any penalties for underpaying throughout the year by paying the safe harbor of the amount I owed from the prior tax year. Then I could pay any extra I owed all in April 2023 with no penalties.

However, I expect my income to fall drastically in 2023 (probably a 30% to 50% drop from 2022). So the safe harbor doesn't make sense in this case since I would be way overpaying. However, it's still hard to know exactly how much I'm going to make next year, so even my best estimate could be decently far off what I actually make.

How do you handle quarterly tax payments when you can't use the safe harbor and you don't know how much you're going to make? I'm just trying to avoid any penalties.

I'm in the US.