Answer:
It depends on what you put into it. Here are the basics of what go into common milkshakes. Take the ingredents that you use, and try to figure it out accordingly.
Banana = 100 calories
Milk = 130 calories
Ice Cream (vanilla / banana, commonly) = 150 calories
Yogurt = 100 to 150 calories (depends on kind)
Granola = 100 calories
Sugar = 15 calories (per teaspoon)