there can be several different reasons for a penalty, even if you are getting a refund.
1) A payment of estimated tax was not timely.
2) 1/4 of your annual withholding + timely estimated tax payments were less than 25% 0f the minimum required payment for each period
rather than using 1/4 of annual withholding for each period, the default, you can check box D on the 2210 and enter actual withholding for each period to see if this reduces or eliminates the penalty.
