Hi BSB
Thanks for the info. I was aware that c4 was a circular reference, but the baffling thing is the formula actually works on google sheets! However, I prefer excel, I read somewhere that it could be something to do with iterations, but my understanding of excel formulas is at the basic level. I have tried using < than, > than without success, but I will keep plugging away.
Thanks anyway
Easygoingdave