| Since you have missed the 2 required quarterly estimated tax payments you could be subjected to both the underpayment penalty and the interest on the underpayment. But, you may have avoided this penalty if you:
1) owe less than $1,000 in tax after subtracting your withholdings and credits.
2) 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.
There are 2 additional circumstances that the IRS will accept and waive the penalties and interest if the following situations apply to you as follows:
1) The failure to make estimated payments was caused by a casualty, disaster, or other unusual circumstance and it would be inequitable to impose the penalty.
2) You retired (after reaching age 62) or became disabled during the tax year for which estimated payments were required to be made or in the preceding tax year, and the underpayment was due to reasonable cause and not willful neglect. | 
