I think you are talking about the estimated tax penalty on 1040 line 24? It's form 2210.
If you do not pay enough tax, you may have to pay a penalty for underpayment of estimated tax. Even if you are getting a refund you can still owe a penalty for not paying in evenly during the year. Generally, most taxpayers will avoid this penalty if they owe less than $1,000 in tax after subtracting their withholdings and credits, or if they paid at least 90% of the tax for the current year, or 100% of the tax shown on the return for the prior year, whichever is smaller. It is included in your tax due or reduces your refund.
You might be able to eliminate it or at least reduce it. You can go to Federal Taxes tab under Other Tax Situations and select Start by the Underpayment Penalties. You will answer a series of questions that may reduce or eliminate the penalty. Or you can elect to have the IRS figure the penalty for you. It's form 2210.
Federal or Personal (for H&B version)
Other Tax Situations
Additional Tax Payments
Underpayment Penalties - Click the Start or update button
If you have the desktop program you can switch to Forms Mode (click forms in the upper right (left for Mac)) and open the 2210 form. If the 2210 doesn't show up in the left column, click on Open Forms at the top of the left column. Type 2210 in the search box and open the 2210 form. Check box C to have the IRS calculate it for you.
ps....I had a refund once and still had a penalty for not paying in evenly during the year.
Adding to VolvoGirl's explanation, underpayments are calculated for each tax quarter of the year. An estimated tax payment made late in the year will not eliminate any penalty for underpayment during the earlier quarters of the year. As VolvoGirl mentioned, if a large portion of your income occurred late in the year, annualizing income on Form 2210AI will likely reduce or eliminate the penalty. However, if a large portion of your income occurred early in the year, annualizing is likely to increase your penalty.