Long story short I just realized yesterday that I mistakenly failed to report a stock sale in which I made about $1000 on my 2009 tax return. This was completely unintentional on my part, but it was definitely my own error.
My question is do I really need to file an amended return? And if so will I be charged any penalties or interest? I'd hate to have to pay a bunch of extra fees for failing to pay a measly $150 in taxes, but at the same time I know it's probably unlikely that anything would become of it if I just continued to ignore it. Again, it was completely unintentional so its not like I filed a fraudulent return.
I'm not asking for legal advice. I know legally now that I have found the mistake I should file the amended return. I'm basically just asking what the likelihood is that anything would become of this if I did nothing or if I did file the amended return how much extra would my total tax bill be.