Client has Qtr. Est. Payments ($4,300 )even throughout the year.  However, they now are planning to convert $35k to ROTH.  If they don't withhold from the conversion and instead make a 1 time payment from their own funds to IRS now and continue with regular estimated payments will the first Qtr. Est that has already been paid be penalized for underpayment?  Essentially with the new AGI from the conversion being $35k higher the estimates would have been $5,400 each qtr.  Now though they would have paid $4300 (Q1) $8400+4300 (Q2) +$4300 (Q3)$4300 (Q4).