In Fall 2024, I calculated the safe harbor by multiplying 1.1 by my total tax from 2023. I then looked at my paystub and extrapolated what I thought I'd pay in taxes through the rest of 2024, and it seemed like I was comfortably over the safe harbor amount. But as I'm doing my taxes now, TurboTax is saying I'll have a modest underpayment penalty. How can I improve the way I'm calculating my numbers so I don't incur another penalty next year? For example, maybe I didn't look at the correct lines on my paystub, or maybe I didn't factor in that some items get maxed out towards the end of the year, resulting in larger year-end paychecks? Or maybe there's some other way to avoid underpaying?
