I reckoned i was over complicating things a bit! Have spent a couple of days online trying to solve the problem!

The main problem is when I try to subtract one date/time from another date/time in the same month, the answer is right.

When I subtract one date/time from another date/time in different months/years, the answer is way wrong.

Then each month I have to get an average turnaround time of each column - and this is when I get the error message....

I had already custom formated the columns as "dd" Days "hh" Hours "mm" mins - should I change this?

I Had originally thought when I started getting these stats it would be a simple A2-A1 to get the difference and then use the AVERAGE() to get the average time - but nothing is ever simple with excel I have discovered!!