Sorry for the mistake with the code, thank you for fixing it. I like the simplicity of your code, but as this is a spreadsheet used by many, many people, I'm reluctant to add an helper column/check cell that could get overwritten or deleted by the curious and/or careless, but I'm certainly going to try it out to see if it works. Thank you!

I have checked the column and re-checked the date column for blank cells, including deleting everything and starting from scratch but to no avail. Should my formula as it stands work?

Thanks again.