2006 Key Penalty Rates
Failure to File Return	5% per month (Maximum 25%)
Failure to Pay Tax	1/2 of 1% per month (Maximum 25%)
Substantial Understatement	20% (40% gross understatement)
Failure to Supply Social Security No.	$50 per occurrence

If your return is filed late without reasonable cause, the IRS may impose a penalty of 5% of the net tax due for each month the return is late, with a maximum penalty of 25%. If the return is more than 60 days late, the penalty will not be less than the smaller of $100 and 100% of the tax due.