Particularly because my Q4 income can vary wildly due to unpredictable year-end mutual fund distributions, I make estimated tax payments to guarantee meeting the safe-harbor of 100% (or110%) of the precious year's tax liability. That might mean overpaying for the earlier quarters, but it avoids a possible need to prepare Schedule AI. I have about a 30-page federal tax return and preparing Schedule AI still more than doubles the effort needed to prepare the entire tax return. I'm willing to pay taxes a bit early to avoid the possibility of having to prepare Schedule AI.
