Thank you. I suppose that the rules are straightforward enough. As long as I have made estimated payments equal to the lesser of at least 90% of the tax owed for the current year (I have not), or 100% of the tax shown on the return for the prior year (which I suppose I have, because last year I got a refund), then I am in compliance. I am simply uncomfortable with making no estimated tax payments this year simply because I got a refund last year, when this year's tax liability will be quite high because of two non-recurring events.