Hi,
My wife (married, jointly) had a $48K windfall at the end of 2014. We knew we would receive it sometime in December, and we paid the feds $12K for the taxes that would be due. But, I completely forgot to pay the state of California. I figured I'd do it when I got the K-1, but I didn't get that until March 20th, but which time the deadline to pay had passed. As a result, our underpayment with CA is about $3.5K. I was going to calculate the underpayment penalty with the H&R software, and I got quite a ways along, but the data required kept coming and coming. You know, income, withholding, adjustments claimed, deductions claimed, all have to be calendarized into three time spans, Jan-Mar, Jan-May, and Jan-Aug. Who knows what else I would have had to calendarize, but after making my fourth spreadsheet, I went back and clicked, "let the FTB calculate my penalty".
I suspect the penalty would be less if I did the calculations, since I know the underpayment was in December, and not spread out all over 2014.
Live and learn.