Comparing cells of two Worksheets
The short answer is don't use VBA at all. Use native Excel formulas. We like to code, so it's natural that we all too often reach for the IDE when we should be heading to the formula bar.

Consider sheet Data_new



And sheet Data_old



You can use a VLookup from Data_old to find the corresponding values in DataNew.

=VLOOKUP(Data_new!$A2,Data_new!$A:$B,2,FALSE)


And then wrap the lookup in an IF formula to populate the final result.

=IF(B2 = VLOOKUP(Data_new!$A2,Data_new!$A:$B,2,FALSE),"OK","NOK")


resulting in the new &amp; improved sheet Data_old.