I thought of that and was left wondering if the efiled amended return would then cancel the efiled original 1st qtr est payment entirely. So I am having the client mail in the 1040x which of course take months to process, and either mail in the additional tax payment separately to a payment center or do it at IRS Direct Pay, choice is theirs. Advised that paying the estimated difference in a separate payment while there brings it to even on that front. This way date stamps beat the deadline but the original efiled return processes as is. I made the client new vouchers for qts 2,3 and 4 with choices for the 2nd qtr determined on whether they made up the shortfall or not at Direct Pay.