Thank you, Vanessa!
I do not remember which form I filed first. However, it is highly likely that it was NY (as it comes as a free state to fill and file in TurboTax; the NJ state return you need to purchase separately). It is highly unlikely that I would enter that NJ total tax number by myself as I would remember why (and how) I did it. It is highly likely that TurboTax, based on the NJ W2 income, estimated a possible NJ tax and assign it on its own to that field in IT-112-R. The thing is that I do not remember that it ever asked me to validate the number that it provided automatically. If this is the case -- this is a clear limitation of TurboTax which can lead to potential troubles for the clients who use it. Indeed, now I need to pay not only the difference but also a quite big penalty to NY.
Yes, I got the notice from NY about this underpayment. Should I request Intuit to cover the penalty payment? That would be logical -- I did not do anything wrong it seems to me.
I tried to calculate all possible differences and could not find the one that matches TurboTax estimate for NJ tax. If I only knew that TurboTax software can do something like this I would double and triple check the return.
