You will not get a penalty notice when you make the late payment. A penalty for making an estimated tax payment late is not automatic. There won't necessarily be a penalty at all. It depends on how your tax return works out at the end of the year. The penalty, if any, will be imposed on your tax return (or after you file your tax return). At the time that you make the late estimated tax payment it is not possible to determine with any certainty whether there will be a penalty.