I am remiss in not having wished my Orthodox brothers and sisters a blessed Easter: It's about time you catch up with our celebration (of course, because you started later, yours will go longer).
I have looked into how to determine the date for Easter for Orthodox of the old calendar, and I came across this site (begin at sectioin 2.13), which provides a calculus for both East and West. Let me tell you that after trying to work through the math, I am determined simply to look it up every year!
It's good for all Christians to be able to sing out together, East nd West, with confidence, "The Lord is risen!" and to reply, "He is risen indeed, alleluia!"