Here are some of the penalties if ever you forget to file or if you filed the incorrect (either intentional or unintentional) tax returns:
For unpaid taxes, penalty is ½ to 1% of taxes unpaid for each month or part of the month after the tax due date. For filing late, penalty is 5% per month of net tax due up to 25%. If the tax return is late for more than 60 days, the minimum penalty is $100 or 100% of tax owed, whichever is lower. For inaccurate returns, maximum penalty is 20% for underpayments that greatly understate income tax (underestimating by at least $5,000 or 10% of the correct tax). Taxpayers who can give reasonable cause for not filing, for filing late, or for filing inaccurate returns may be excuse from paying the penalty.
And lastly, for fraud, the penalty is 15% for each whole and part month with a maximum penalty is 75%.