If you didn’t pay enough tax throughout the year, either through withholding or by making estimated tax payments, unfortunately you may have to pay a penalty for underpayment of estimated tax.
The IRS impose an interest penalty if you underpay your taxes. The interest is based on the difference between the amount you should have paid for each installment and the amount you actually paid for as long as the underpayment remains outstanding.
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. Also, There are special rules for farmers and fishermen.