Thank you so much for taking the time to look at my question - I don't know what I did but I fixed it and it is working now!Thanks anyway

I hope this is what you mean, thank you for your help. I'm sorry it probably looks very simple/rubbish!

I designed a simple form ages ago and it all worked ok.I now need to update this and added and extra couple of lines but cannot for the life of me get the calculate script to work.There was a column adding up the lines above (on an invoice) and a 'total due' at the bottom.I probably didn't do this r...