Assuming you are working a standard Mon - Fri, the correct amount of weekends to be working is 0.
There is some tradeoff point if you make overtime and you need the money. If you are salaried, then just say no.
I occasionally get asked to work a late night or a weekend. It's never a real emergency - nobody is blocked, it isn't software that impacts live users, etc. It's just scheduling fails by some middle manager somewhere. My answer is always the same:
"Oh, sorry, I can't. Already scheduled."