make a sumif formula dynamic

Hello. Any suggestion on how I can make the following formula dynamic? In E4 and beyond I have a formula that will change the cell from "estimate" to "actual" when I insert a tab with actuals information. Currently in the C column, I have the formula below running through January, because that is what I have actuals through. I would like to make this dynamic so that when actuals comes in, the formula below calculates for two months instead of just one. Thank you.


=IFERROR(SUM($E16)/(SUMIF($B$15:$B$66,$B16,$E$15:E$66)),0%)