Thanks for the quick reply Andrew it works well but what I should have said was what I actually wanted to do, I thought it would be easier just to multiply and I could work the formula out but I can't figure it out! have more lots more to learn... Here below is exactly what I want to do.

I have a value 2100 I want to find 7.5% of the first 75 then find 4% of everything from 76 to 1000 then 3% of everything from 1001 and over, then add those values up and display them in the field.

Thanks for your help.