Originally Posted by Joachim

I have one formfield (cost1)where I multiply two other formfields, works fine.
I have a second formfield (cost2) where I multiply two other formfields, works fine as well.
In a further formfield I add the two products (=cost1+cost2). The result is always the double of the correct number (like 20+10=60 instead of 30).

Originally Posted by macropod

This is a known, long-standing bug in calculation formfields. Use formula fields for the calculations instead.