Hi Carmen, this question pops up all the time. If you search cake decor for this question on blogs you should get some of the answers put up before. Someone did say there is an app called CakeUlater just google it. What I do is work out exactly what it has cost me to make the cake ( everything including electricity or gas) and then times it by 2.5, then if you have a cake that has a lot of fiddley details, modelling, calculate how many hours you have spent doing them and add amount to cover the time spent. I’m only doing this as a hobby so maybe the professionals work it out differently. Hope this helps! :-)
Kath's Cakes https://www.facebook.com/pages/Kaths-Cakes/369485736483786