Avoiding Penalty for Underpayment of Taxes

[larryj]

Last year (2009) I had zero tax liability due to very little income and big losses in the stock market. This year I've been employed and have made about $27,000, but elected to not pay any federal income tax by claiming 9 exemptions on my W-4. Will I get penalized for underpayment? Technically I'm meeting the requirement of paying 100% of 2009's tax liability. Should I send in a estimated tax payment before 1/15/11 to avoid a penalty or is it too late? Thanks for your help. -Larry