there is a calculator link. https://neocoins.net/ this will tell you how many ANCS you will generate by storing your ANS in the web wallet. of course you won't be able to see them if you have a Mac or you know your stuff about opening windows on the Mac. I'm hoping a new wallet comes out soon for the Mac so I can claim the gas it generates.
RE: Officially confirmed + HOW TO - holding Antshares (NEO) in web wallet generates Antcoins (GAS)