Good morning Zagra147

This sounds like you don't want to extract data from a closed workbook, you want to use it in a calculation - these aren't the same thing.

I assume you're trying to use SUMIF (or SUMIFS) formulae? These, unlike most of Excel's other formulae, do not work with closed workbooks. You are correct that you can use SUMPRODUCT on a closed workbook. If you want to go this way, you will need to provide examples of your current formulae as the syntax between SUMIFS and SUMPRODUCT are significantly different. SUMPRODUCT is also significantly slower than its SUMIFS counterpart, so this may not be the way forward, depending how many calculations are required, how big the ranges involved etc.

An alternative is to extract the data from your 12 workbooks into a temporary sheet and do the calculations from the temporary sheet (which can be hidden).

Have a think about what suits your purposes.

HTH

DominicB