Underpayment Penalty(p43)

If you did not pay enough tax, either through withholding or by making estimated tax payments, you will have an underpayment of estimated tax and you may have to pay a penalty.

Generally, you will not have to pay a penalty for 2008 if any of the following situations applies.

• The total of your withholding and estimated tax payments was at least as much as your 2007 tax (or 110% of your 2007 tax if your AGI was more than $150,000, $75,000 if your 2008 filing status is married filing separately) and you paid all required estimated tax payments on time.
• The tax balance due on your return is no more than 10% of your total 2008 tax, and you paid all required estimated tax payments on time.
• Your total 2008 tax minus your withholding is less than $1,000.
• You did not have a tax liability for 2007.
• You did not have any withholding taxes and your current year tax less any household employment taxes is less than $1,000.

Special rules apply if you are a farmer or fisherman. See Farmers and Fishermen in chapter 4 of Publication 505 for more information.

If you think you owe the penalty but you do not want to figure it yourself when you file your tax return, you may not have to. Generally, the IRS will figure the penalty for you and send you a bill. However, if you think you are able to lower or eliminate your penalty, you must complete Form 2210 or Form 2210-F and attach it to your return. See chapter 4 of Publication 505.