Hi,

I have a large data file roughly about 18,000,000 lines. I put in a vlookup function and it took around 15 mins to calculate. When I tried to save the work book, the calculating threads start again.

Is there a way to resolve this issue please?

Thank you

Sorry it's not 18,000,000 lines but 18,000 lines instead.

It depends on you table(s) structure(s), and on your formula. My advice is, post a copy of your workbook with a minimal amount of [mocked up] data (enough of it to get the formula working), and with your formula, here. Without this info, nobody can advice anything!