I agree that waiting to efile until 3/17/22 because of Form 2210 will annoy a lot of clients who are thus obliged to pay an additional months of interest. I will have an enormous pile of ready-to-efile-except-for Form 2210 or 8895 (for all self-employed folks). That's half of my clients. Just on the date that corps and partnerships are due, and all brokerage 1099s arrive. That leaves one month to do it all.