Why did the IRS charge an underpayment of estimated tax penalty even though this taxpayer paid 95% of their 2025 tax bill by January 15, 2026? The problem is that estimated taxes generally aren’t judged only by how much you’ve paid by the end of the year. When you made those payments can matter too. In this video, I explain why making a large estimated tax payment late in the year may not eliminate penalties from earlier quarters, how the estimated tax safe harbors work, and when IRS Form 2210 and the annualized income installment method may help taxpayers whose income wasn’t earned evenly throughout the year. I cover: Why paying 90%+ of your tax doesn’t automatically eliminate an estimated tax penalty How the IRS looks at estimated payments throughout the year What happens when you make most of your payment in Q4 When uneven or seasonal income can change the calculation How Form 2210 can potentially reduce or eliminate an underpayment penalty Why taxpayers with back-loaded income ...