This year, we got back a good chunk of money from the feds, and I had calculated that we'd owe the state about $1300, which I was saving until April.
I use taxslayer.com to file our federal returns electronically and get our refunds quickly, then in April I add up the figures from taxslayer.com and write them on a mail-in copy of the Massachusetts form (again, since we end up owing, I like to do it the slow way involving a paper copy and a check, which usually takes them about a month to enter and cash). I usually tell taxslayer.com to calculate the Massachusetts returns, so I don't have to think about what to put on which line, but then I leave off some of the state-specific information on the state return so it will come back with an error message and only send off the federal ones.
This year, I left off the health insurance policy number, along with the rest of the Massachusetts-specific questions. I had checked the box that, yes, we had health insurance all year and weren't subject to the penalty for not having it.
Just now, when I went to transfer the figures off of the .pdf from taxslayer.com, I got down to the last few lines of the return and realized it had been penalizing both of us for not having health insurance. So we actually don't owe $1300; we owe $30. Even better is that the $1300 is sitting in the bank waiting to go to the tax people. Now it's going to go to IKEA.
I should make stupid mistakes on my taxes more often.